Prevent stamping a commit if there are pending changes in the tree.

Review Request #6712 — Created Dec. 31, 2014 and submitted — Latest diff uploaded

Information

RBTools
master
a74c9d5...

Reviewers

When running rbt stamp with any pending changes in the index, those
changes could end being amended into the commit. We now check for
pending changes before attempting to stamp.

Made a change to the tree and tried to stamp a commit. Saw the error
instead.