message: Don't look for source.properties to check valid SDK path
  * This file isn't always there apparently. Instead just look for a build-tools
  folder which must be present.
diff: @@ -7,11 +7,11 @@ if(BUILD_ANDROID)
  endif()
  message(STATUS "Using JAVA_HOME = $ENV{JAVA_HOME}")
  - if(DEFINED ENV{ANDROID_HOME} AND EXISTS "$ENV{ANDROID_HOME}/platform-tools/source.properties")
  + if(DEFINED ENV{ANDROID_HOME} AND EXISTS "$ENV{ANDROID_HOME}/build-tools")
  set(ANDROID_SDK_ROOT_PATH "$ENV{ANDROID_HOME}")
  - elseif(DEFINED ENV{ANDROID_SDK_ROOT} AND EXISTS "$ENV{ANDROID_SDK_ROOT}/platform-tools/source.properties")
  + elseif(DEFINED ENV{ANDROID_SDK_ROOT} AND EXISTS "$ENV{ANDROID_SDK_ROOT}/build-tools")
  set(ANDROID_SDK_ROOT_PATH "$ENV{ANDROID_SDK_ROOT}")
  - elseif(DEFINED ENV{ANDROID_SDK} AND EXISTS "$ENV{ANDROID_SDK}/platform-tools/source.properties")
  + elseif(DEFINED ENV{ANDROID_SDK} AND EXISTS "$ENV{ANDROID_SDK}/build-tools")
  set(ANDROID_SDK_ROOT_PATH "$ENV{ANDROID_SDK}")
  else()
  message(FATAL_ERROR "Can't locate Android SDK, set ANDROID_HOME, ANDROID_SDK_ROOT or ANDROID_SDK")
  