git-gui: Cleanup bindings within merge dialog
git-gui: Cleanup bindings within merge dialog

Misc. code cleanups in the merge dialog's binding setup and action
button creation.

Signed-off-by: Shawn O. Pearce <f01032651c12a22b2103346ba96b3b6b231f9d3c@spearce.org>
destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git