title: Add different proguard file for debug
body: <p>I have a project with two modules. It exists a default configuration of build.gradle:</p>
  
  <pre><code>buildTypes {
          release {
              minifyEnabled true
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
      }
  </code></pre>
  
  <p>And I want to add a different configuration (proguard and minifying) for debug compilation as follow:</p>
  
  <pre><code>buildTypes {
          release {
              minifyEnabled true
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
          debug {
              minifyEnabled false
              proguardFiles 'proguard-rules-debug.pro'
          }
      }
  </code></pre>
  
  <p>When I put this code in my project, it doesn't compile. The log show a message error for each reference to another module:</p>
  
  <pre><code>Error:(37, 42) error: package com.example does not exist
  </code></pre>
  
  <p>Full Gradle configuration of the two modules.</p>
  
  <p>The app module:</p>
  
  <pre><code>buildscript {
      repositories {
          maven { url 'https://maven.fabric.io/public' }
      }
  
      dependencies {
          ...
      }
  }
  
  apply plugin: 'com.android.application'
  ...
  
  android {
      compileSdkVersion 23
      buildToolsVersion "23.0.3"
  
      defaultConfig {
          ...
          minSdkVersion 16
          targetSdkVersion 23
          versionCode 1
          versionName "1.3"
      }
      buildTypes {
          release {
              minifyEnabled true
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
          debug {
              minifyEnabled false
          }
      }
  }
  
  repositories {
      maven {
          ...
      }
  }
  
  repositories{
      maven {
          url 'http://dl.bintray.com/amulyakhare/maven'
      }
  }
  
  ...
  
  dependencies {
      ...
  }
  </code></pre>
  
  <p>The library module:</p>
  
  <pre><code>apply plugin: 'com.android.library'
  
  android {
      compileSdkVersion 24
      buildToolsVersion "24.0.1"
  
      defaultConfig {
          ...
      }
      buildTypes {
          release {
              minifyEnabled true
              proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
          }
          debug {
              minifyEnabled false
          }
      }
  }
  
  dependencies {
      compile fileTree(dir: 'libs', include: ['*.jar'])
      ...
  }
  </code></pre>