revset: strip off "literal:" prefix from bookmark not found error

This is what branch() and tag() do.

mercurial/revset.py

@@ -696,7 +696,7 b' def bookmark(repo, subset, x):'
             bmrev = repo._bookmarks.get(pattern, None)
             if not bmrev:
                 raise error.RepoLookupError(_("bookmark '%s' does not exist")
-                                            % bm)
+                                            % pattern)
             bms.add(repo[bmrev].rev())
         else:
             matchrevs = set()

tests/test-bookmarks.t

@@ -135,6 +135,9 b' bookmarks revset'
   $ hg log -r 'bookmark(unknown)'
   abort: bookmark 'unknown' does not exist!
   [255]
+  $ hg log -r 'bookmark("literal:unknown")'
+  abort: bookmark 'unknown' does not exist!
+  [255]
   $ hg log -r 'bookmark("re:unknown")'
   abort: no bookmarks exist that match 'unknown'!
   [255]