Fix #6 : use HEAD branch instead of master by default

By default the "Check out Maven Projects from SCM" wizard displays a "Check out HEAD Revision" label, but the default branch is always set to master.

This prevents the maven project from git://github.com/jboss-jdf/ticket-monster.git from being imported (see https://issues.jboss.org/browse/JBIDE-17446), as the master branch doesn't exist.

The fix simply sets the branch name to HEAD instead of master by default.

Signed-off-by: Fred Bricon <fbricon@gmail.com>