Squashed commit of the following:

commit f3f981022f9157e9d74a9d9dfef7ae102c4d0593
Author: rfscholte <rfscholte@apache.org>
Date:   Thu Feb 9 11:00:17 2017 +0100

    [MNG-6109] PluginDescriptor doesn't read since value of parameter
    There's no specific IT, just a unittest, so itBranch should stay on master

commit 862e8e4e3a2b857eeeb4761a1568c15ebb442932
Author: rfscholte <rfscholte@apache.org>
Date:   Wed Feb 8 21:55:30 2017 +0100

    [MNG-6109] PluginDescriptor doesn't read since value of parameter

commit 76b539ecf2733b2a8564c18581d60176dc0185a3
Author: rfscholte <rfscholte@apache.org>
Date:   Mon Oct 31 21:05:28 2016 +0100

    PluginDescriptor doesn't read since value of parameter

maven-plugin-api/src/main/java/org/apache/maven/plugin/descriptor/PluginDescriptorBuilder.java

@@ -299,6 +299,8 @@ public class PluginDescriptorBuilder
 
             parameter.setImplementation( d.getChild( "implementation" ).getValue() );
 
+            parameter.setSince( d.getChild( "since" ).getValue() );
+
             PlexusConfiguration paramConfig = mojoConfig.getChild( parameter.getName(), false );
             if ( paramConfig != null )
             {

maven-plugin-api/src/test/java/org/apache/maven/plugin/descriptor/PluginDescriptorBuilderTest.java

@@ -108,6 +108,7 @@ public class PluginDescriptorBuilderTest
         assertEquals( "deprecated-parameter", mp.getDeprecated() );
         assertEquals( "${jar.finalName}", mp.getExpression() );
         assertEquals( "${project.build.finalName}", mp.getDefaultValue() );
+        assertEquals( "3.0.0", mp.getSince() );
 
         ComponentRequirement cr = md.getRequirements().get( 0 );
 

maven-plugin-api/src/test/resources/plugin.xml

@@ -60,6 +60,7 @@ under the License.
           <editable>true</editable>
           <description>parameter-description</description>
           <deprecated>deprecated-parameter</deprecated>
+          <since>3.0.0</since>
         </parameter>
       </parameters>
       <configuration>