Message generation breaks if git branch name ends with .msg

[svanderweyst-cpr]

The message generation traverses all directories of the ros package looking for files that match the name *.msg
Creating a git branch with the name break-it.msg will create files like
.git/refs/remotes/origin/break-it.msg and .git/logs.refs/remotes/origin/break-it.msg
Putting a CATKIN_IGNORE into the .git directory mitigates this problem.

It would be very handy to be able to either specify which directories to scan for messages, or to be able to exclude certain directories more easily (like source control directories)