strip: do not update branchcache during strip (issue3745)

At this moment, the cache is invalid, and will be thrown away.
Later the strip function will call the `localrepo.destroyed` method
that will update the branchmap cache.

mercurial/localrepo.py

@@ -2395,6 +2395,10 b' class localrepository(object):'
             tr.close()
 
             if changesets > 0:
+                if srctype != 'strip':
+                    # During strip, branchcache is invalid but coming call to
+                    # `destroyed` will repair it.
+                    # In other case we can safely update cache on disk.
                 branchmap.updatecache(self)
                 def runhooks():
                     # forcefully update the on-disk branch cache

tests/test-keyword.t

@@ -507,7 +507,6 b' amend'
   $ hg -q commit -d '14 1' -m 'prepare amend'
 
   $ hg --debug commit --amend -d '15 1' -m 'amend without changes' | grep keywords
-  invalidating branch cache (tip differs)
   overwriting a expanding keywords
   $ hg -q id
   67d8c481a6be