bookmarks: update and updatecurrentbookmark return status

This makes bookmarks.update() and bookmarks.updatecurrentbookmark() return
True or False to indicate whether the bookmark was updated or not. This allows
callers to e.g. abort if the update failed.

mercurial/bookmarks.py

@@ -128,10 +128,10 b' def setcurrent(repo, mark):'
 
 def updatecurrentbookmark(repo, oldnode, curbranch):
     try:
-        update(repo, oldnode, repo.branchtags()[curbranch])
+        return update(repo, oldnode, repo.branchtags()[curbranch])
     except KeyError:
         if curbranch == "default": # no default branch!
-            update(repo, oldnode, repo.lookup("tip"))
+            return update(repo, oldnode, repo.lookup("tip"))
         else:
             raise util.Abort(_("branch %s not found") % curbranch)
 
@@ -147,6 +147,7 b' def update(repo, parents, node):'
             update = True
     if update:
         repo._writebookmarks(marks)
+    return update
 
 def listbookmarks(repo):
     # We may try to list bookmarks on a repo type that does not