Support empty directory creation

ARCHETYPE-57 was never really resolved. As of alpha-4 and alpha-5 empty directories are not included in the archetype JAR files. There seem to be two issues:

1) – Edit/clarification: Doesn't seem to be necessary.

2) The archetype archiver/JAR goal does not include empty directories unless explicitly listed in the archetype-metadata.xml. You can't apply inclusion wildcards, etc. The JAR mojo should include an includeEmptyDirs option. Additionally, this will require code changes to: archetype-common/src/main/java/org/apache/maven/archetype/DefaultArchetype.java (maybe others as well?)
In particular the archiveArchetype and zipper routines to include empty directories.

e.g. in zipper()
111 {
112 File[] files = currentSourceDirectory.listFiles();
113
114 for ( int i = 0; i < files.length; i++ )
115 {
116 if ( files[i].isDirectory() )
117 {
118 zipper( zos, offset, files[i] );

This area should have a check for if(includeEmptyDirs && files.length == 0)

archetype.xml is for Archetype 1.0.x: nothing will be fixed there

archetype-metadata.xml is for Archetype 2.0.x: if you provide a test case that I can reproduce, I'll work on a fix

Herve, the attached zip file should show the issue. src/main/webapp is included in the generated artifact, as per the archetype-metadata.xml, but none of it's (empty) subdirectories is.

first pass in r1159926
this is actually limited to non-filtered filesets, I still need to investigate if it is reasonably extensible to filtered filesets (which actually creates an empty file instead of an empty directory)

notice that you must configure includeEmptyDirs=true for maven-resources-plugin or the archetype jar won't contain the empty directory (then of course the project generated from the archatype can't contain it...)

filtered support added in r1159957

IT support (comparison against reference) added in r1159975