Break undo only if a snippet gets expanded.

Instead of creating a new undo point always, this gets done now only if
a snippet gets expanded.
This means that "foobarbaz<tab>" won't break undo (with a non-change
point).

See the discussion at
MarcWeber@73a7255

after/plugin/snipMate.vim

@@ -10,7 +10,7 @@ let s:did_snips_mappings = 1
 "
 " You can safely adjust these mappings to your preferences (as explained in
 " :help snipMate-remap).
-ino <silent> <tab> <c-g>u<c-r>=TriggerSnippet()<cr>
+ino <silent> <tab> <c-r>=TriggerSnippet()<cr>
 snor <silent> <tab> <esc>i<right><c-r>=TriggerSnippet()<cr>
 ino <silent> <s-tab> <c-r>=BackwardsSnippet()<cr>
 snor <silent> <s-tab> <esc>i<right><c-r>=BackwardsSnippet()<cr>

plugin/snipMate.vim

@@ -83,6 +83,7 @@ fun! TriggerSnippet()
 		" If word is a trigger for a snippet, delete the trigger & expand
 		" the snippet.
 		if snippet != ''
+			let &undolevels = &undolevels " create new undo point
 			let col = col('.') - len(trigger)
 			sil exe 's/\V'.escape(trigger, '/\.').'\%#//'
 			return snipMate#expandSnip(snippet, col)