Added amend option to commit operation
Merge branch 'amend' of git://github.com/volaya/GeoGit into volaya-amend

Conflicts resolved:
	src/cli/src/main/java/org/geogit/cli/porcelain/Commit.java
	src/core/src/main/java/org/geogit/api/porcelain/CommitOp.java
	src/core/src/test/java/org/geogit/test/integration/CommitOpTest.java
Merge branch 'volaya-amend'