title: Installing libgtk-3-dev, unmet dependencies
body: <p>I'm trying to install seahorse-3.16.0. When running ./configure, I get:</p>
  
  <pre><code>configure: error: Package requirements (gtk+-3.0 &gt;= 3.4.0) were not met:
  
  No package 'gtk+-3.0' found
  
  Consider adjusting the PKG_CONFIG_PATH environment variable if you
  installed software in a non-standard prefix.
  
  Alternatively, you may set the environment variables GTK_CFLAGS
  and GTK_LIBS to avoid the need to call pkg-config.
  See the pkg-config man page for more details.
  </code></pre>
  
  <p>I've tried installing libgtk-3-dev with:</p>
  
  <pre><code>sudo apt-get install libgtk-3-dev
  </code></pre>
  
  <p>Here's the output:</p>
  
  <pre><code> Reading package lists... Done
   Building dependency tree       
   Reading state information... Done
   Some packages could not be installed. This may mean that you have
   requested an impossible situation or if you are using the unstable
   distribution that some required packages have not yet been created
   or been moved out of Incoming.
   The following information may help to resolve the situation:
  
   The following packages have unmet dependencies:
    libgtk-3-dev : Depends: libglib2.0-dev (&gt;= 2.37.5) but it is not going to be installed
                   Depends: libgdk-pixbuf2.0-dev (&gt;= 2.27.1) but it is not going to be installed
                   Depends: libpango1.0-dev (&gt;= 1.32.4) but it is not going to be installed
                   Depends: libatk1.0-dev (&gt;= 2.7.5) but it is not going to be installed
                   Depends: libatk-bridge2.0-dev but it is not going to be installed
                   Depends: libcairo2-dev (&gt;= 1.13.0~20140204) but it is not going to be installed
   E: Unable to correct problems, you have held broken packages.
  </code></pre>
  
  <p>I've tried installing individual packages but they boil down to depending on something that is already present and all the way up to date. I've also tried installing libgtk-3-dev with aptitude, and I've run sudo apt-get update and sudo apt-get upgrade numerous times. </p>
  
  <p>Any and all help is appreciated. </p>