keyword: mimic cmdutil.bail_if_changed even more

At the check before overwriting with kwexpand, kwshrink:
- abort when in middle of merge
- give terser abort message

hgext/keyword.py

@@ -263,11 +263,13 b' def _status(ui, repo, kwt, *pats, **opts'
 
 def _kwfwrite(ui, repo, expand, *pats, **opts):
     '''Selects files and passes them to kwtemplater.overwrite.'''
+    if repo.dirstate.parents()[1] != nullid:
+        raise util.Abort(_('outstanding uncommitted merge'))
     kwt = kwtools['templater']
     status = _status(ui, repo, kwt, *pats, **opts)
     modified, added, removed, deleted, unknown, ignored, clean = status
     if modified or added or removed or deleted:
-        raise util.Abort(_('outstanding uncommitted changes in given files'))
+        raise util.Abort(_('outstanding uncommitted changes'))
     wlock = lock = None
     try:
         wlock = repo.wlock()

tests/test-keyword.out

@@ -350,7 +350,7 b' 1 files updated, 0 files merged, 0 files'
 % kwexpand a
 overwriting a expanding keywords
 % kwexpand x/a should abort
-abort: outstanding uncommitted changes in given files
+abort: outstanding uncommitted changes
 x/a
  x/a: copy a:779c764182ce5d43e2b1eb66ce06d7b47bfe342e
 overwriting x/a expanding keywords