title: Gradle fails after converting project into module
body: <p>I'm trying to integrate the PDFNet library into my Android App, and if you download the SDK you can see that there is a project CompleteReader (PDFNetAndroid-6.7.0.42960\PDFNetAndroid\samples\PDFViewCtrlProjects\CompleteReader)
  I want to use this project as a module in my app so I changed in build.gradle "com.android.application" to "com.android.library"</p>
  
  <p>Here the original build.gradle:</p>
  
  <pre><code>description = 'This is a more complete demo app that showcases PDFViewCtrl and the Tools library and its controls.'
  
  apply plugin: 'com.android.application'
  
  repositories {
      mavenCentral()
  }
  
  buildscript {
      repositories {
          mavenCentral()
          jcenter()
      }
  
      dependencies {
          classpath 'com.android.tools.build:gradle:1.3.0'
          classpath 'com.trello:victor:0.1.4'
      }
  }
  
  apply plugin: 'com.android.application'
  apply plugin: 'com.trello.victor'
  
  
  dependencies {
      compile fileTree(include: '*.jar', dir: 'libs')
      compile project(':PDFViewCtrlTools')
      compile 'com.android.support:appcompat-v7:23.1.1'
      compile 'com.android.support:design:23.1.1'
      compile 'com.jakewharton:butterknife:7.0.1'
      compile 'com.tonicartos:superslim:0.4.13'
  }
  
  android {
      compileSdkVersion 23
      buildToolsVersion "23.0.2"
  
      defaultConfig {
          minSdkVersion 16
          targetSdkVersion 23
          versionCode 1
          versionName "1.0.0"
      }
  
      sourceSets {
          main {
              manifest.srcFile 'AndroidManifest.xml'
              java.srcDirs = ['src']
              resources.srcDirs = ['src']
              res.srcDirs = ['res']
              jniLibs.srcDirs = ['libs']
              svg.srcDir 'src/main/svg'
          }
      }
  
      buildTypes {
          release {
              minifyEnabled true
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-project.txt'
          }
          debug {
              // Set package name to &lt;app package&gt;.debug to be able to install both debug and release apk on the same device
              applicationIdSuffix ".debug"
          }
      }
  
      lintOptions {
          // If true, stop the gradle build if errors are found
          abortOnError false
          //ignore 'ValidFragment'
      }
  
      productFlavors {
          armv7a {
              ndk {
                  abiFilters "armeabi-v7a"
              }
          }
          arm {
              ndk {
                  abiFilters "armeabi"
              }
          }
          x86 {
              ndk {
                  abiFilters "x86"
              }
          }
          armv8 {
              ndk {
                  abiFilters "arm64-v8a"
              }
          }
          x86_64 {
              ndk {
                  abiFilters "x86_64"
              }
          }
          fat {
              ndk {
                  abiFilters "armeabi-v7a", "armeabi", "arm64-v8a", "x86", "x86_64"
              }
          }
      }
  }
  task copyLibsToSamples &lt;&lt; {
      ['libs'
       ].each { dest -&gt;
          copy {
              from ('../../../lib/full') {
                  include '**/*.so'
              }
              into dest
          }
       }
  }
  
  task copyJarToSamples(type: Copy) {
      ['../../../lib/src/PDFViewCtrlTools/libs'
       ].each { dest -&gt;
          copy {
              from ('../../../lib') {
                  include 'PDFNet.jar'
              }
              into dest
          }
       }
  }
  
  task copyResources &lt;&lt; {
      ['res/raw'].each { dest -&gt;
          copy {
              from ('../../../resource') {
                  include '*.plugin'
              }
              into dest
          }
      }
  }
  
  task setupSample(dependsOn: [copyLibsToSamples, copyJarToSamples, copyResources])
  
  preBuild.dependsOn setupSample
  </code></pre>
  
  <p>This original file compiles without problem, but with the change to library it won't build, so I removed following that I read somewhere could be the problem:</p>
  
  <pre><code>repositories {
      mavenCentral()
  }
  </code></pre>
  
  <p>Ok, with this change it seems that the build can continue, the next errors I got was with following two references that could not be resolved (this all works when the original file is not modified!!!):</p>
  
  <pre><code>compile 'com.jakewharton:butterknife:7.0.1'
  compile 'com.tonicartos:superslim:0.4.13'
  </code></pre>
  
  <p>I tried so many things in this file already a few days without luck, I removed all parts that could not be needed, moved jcenter and mavencentral around, added them, removed them, etc. 
  This is my current build.gradle that also does not work:</p>
  
  <pre><code>description = 'This is a more complete demo app that showcases PDFViewCtrl and the Tools library and its controls.'
  
  buildscript {
      repositories {
          jcenter()
      }
  
      dependencies {
          classpath 'com.android.tools.build:gradle:2.1.0'
          classpath 'com.trello:victor:0.1.4'
      }
  }
  
  apply plugin: 'com.android.library'
  apply plugin: 'com.trello.victor'
  
  dependencies {
      repositories {
          mavenCentral()
          jcenter()
      }
      compile fileTree(include: '*.jar', dir: 'libs')
      compile project(':PDFViewCtrlTools')
      compile 'com.android.support:appcompat-v7:23.4.0'
      compile 'com.android.support:design:23.4.0'
      compile project(':superslim-0.4.13')
      compile 'com.jakewharton:butterknife:7.0.1'
  }
  
  android {
      compileSdkVersion 23
      buildToolsVersion "23.0.3"
  
      sourceSets {
          main {
              manifest.srcFile 'AndroidManifest.xml'
              java.srcDirs = ['src']
              resources.srcDirs = ['src']
              res.srcDirs = ['res']
              jniLibs.srcDirs = ['libs']
              svg.srcDir 'src/main/svg'
          }
      }
  
      lintOptions {
          // If true, stop the gradle build if errors are found
          abortOnError false
          //ignore 'ValidFragment'
      }
  }
  
  task wrapper(type: Wrapper) {
      gradleVersion = '2.2'
  }
  </code></pre>
  
  <p>It does not matter what I change, the module can't be compiled, I get Execution failed for task CompleteReader:compileDebugJavaWithJavac and R is not being generated so I get a lot of "constant expression required". I repeat, before changing "application" to "library" all work fine, I can install the project on my phone, etc.</p>
  
  <p>Do you have any ideas what's wrong? I am already working 3 days on this without luck!</p>