Fix a "property not found" exception in Gradle 2.x

libraries/tools/kotlin-gradle-plugin-core/src/main/kotlin/org/jetbrains/kotlin/gradle/tasks/Tasks.kt

@@ -101,8 +101,9 @@ public open class KotlinCompile() : AbstractKotlinCompile<K2JVMCompilerArguments
     val srcDirsSources = HashSet<SourceDirectorySet>()
 
     override fun populateTargetSpecificArgs(args: K2JVMCompilerArguments) {
-        args.pluginClasspaths = property("compilerPluginClasspaths") as? Array<String>
-        args.pluginOptions = property("compilerPluginArguments") as? Array<String>
+        val extraProperties = getExtensions().getExtraProperties()
+        args.pluginClasspaths = extraProperties.get("compilerPluginClasspaths") as? Array<String>
+        args.pluginOptions = extraProperties.get("compilerPluginArguments") as? Array<String>
 
         if (StringUtils.isEmpty(kotlinOptions.classpath)) {
             val existingClasspathEntries = getClasspath().filter({ it != null && it.exists() })

libraries/tools/kotlin-gradle-plugin/src/main/kotlin/org/jetbrains/kotlin/gradle/plugin/KotlinPlugin.kt

@@ -474,8 +474,9 @@ private class SubpluginEnvironment(
             }
         }
 
-        compileTask.setProperty("compilerPluginClasspaths", realPluginClasspaths.copyToArray())
-        compileTask.setProperty("compilerPluginArguments", pluginArguments.copyToArray())
+        val extraProperties = compileTask.getExtensions().getExtraProperties()
+        extraProperties.set("compilerPluginClasspaths", realPluginClasspaths.copyToArray())
+        extraProperties.set("compilerPluginArguments", pluginArguments.copyToArray())
     }
 }