bookmarks: catch the proper exception for missing revisions

This fixes a regression from 1.7

mercurial/bookmarks.py

@@ -7,7 +7,7 b''
 
 from mercurial.i18n import _
 from mercurial.node import hex
-from mercurial import encoding, error, util
+from mercurial import encoding, util
 import errno, os
 
 def valid(mark):
@@ -36,7 +36,7 b' def read(repo):'
             refspec = encoding.tolocal(refspec)
             try:
                 bookmarks[refspec] = repo.changelog.lookup(sha)
-            except error.RepoLookupError:
+            except LookupError:
                 pass
     except IOError, inst:
         if inst.errno != errno.ENOENT:

tests/test-bookmarks.t

@@ -371,3 +371,8 b' test wrongly formated bookmark'
    * Z                         3:125c9a1d6df6
      x  y                      2:db815d6d32e6
 
+test missing revisions
+
+  $ echo "925d80f479bc z" > .hg/bookmarks
+  $ hg book
+  no bookmarks set