Add new method (postCreateArchive) to AbstractArchiver

The purpose of the method is to allow subclasses
to augment the archive after it is created.
This is going to be used to update Jar archives
to modular Jar archives.

Author: plamentotev

src/main/java/org/codehaus/plexus/archiver/AbstractArchiver.java

@@ -1007,6 +1007,8 @@ public final void createArchive()
         {
             cleanUp();
         }
+
+        postCreateArchive();
     }
 
     protected boolean hasVirtualFiles()
@@ -1036,6 +1038,21 @@ protected void validate()
     {
     }
 
+    /**
+     * This method is called after the archive creation
+     * completes successfully (no exceptions are thrown).
+     *
+     * Subclasses may override this method in order to
+     * augment or validate the archive after it is
+     * created.
+     *
+     * @since 3.6
+     */
+    protected void postCreateArchive()
+        throws ArchiverException, IOException
+    {
+    }
+
     protected abstract String getArchiveType();
 
     private void addCloseable( Object maybeCloseable )