Allow customizing of MANIFEST.MF.

Add test cases for the customization


git-svn-id: https://svn.apache.org/repos/asf/maven/maven-1/plugins/trunk@114957 13f79535-47bb-0310-9956-ffa450edef68

war/plugin.properties

@@ -40,3 +40,5 @@ maven.war.build.dir = ${maven.build.dir}
 # ${maven.war.build.dir}/${pom.artifactId}
 maven.war.webapp.dir = ${maven.war.build.dir}/${pom.artifactId}
 maven.war.tld.dir=WEB-INF/tld
+
+maven.jar.manifest=${pom.build.sourceDirectory}/META-INF/MANIFEST.MF