Make distinct lookup error for localrepo.lookup

This allows clone/share to correctly distinguish lookup errors from
corruption errors and catch only the former.

mercurial/error.py

@@ -36,6 +36,9 b' class ConfigError(Exception):'
 class RepoError(Exception):
     pass
 
+class RepoLookupError(RepoError):
+    pass
+
 class CapabilityError(RepoError):
     pass
 

mercurial/hg.py

@@ -137,10 +137,12 b' def share(ui, source, dest=None, update='
         if update is not True:
             checkout = update
         for test in (checkout, 'default', 'tip'):
+            if test is None:
+                continue
             try:
                 uprev = r.lookup(test)
                 break
-            except LookupError:
+            except error.RepoLookupError:
                 continue
         _update(r, uprev)
 
@@ -309,10 +311,12 b' def clone(ui, source, dest=None, pull=Fa'
                 if update is not True:
                     checkout = update
                 for test in (checkout, 'default', 'tip'):
+                    if test is None:
+                        continue
                     try:
                         uprev = dest_repo.lookup(test)
                         break
-                    except:
+                    except error.RepoLookupError:
                         continue
                 _update(dest_repo, uprev)
 

mercurial/localrepo.py

@@ -509,7 +509,7 b' class localrepository(repo.repository):'
                 key = hex(key)
         except:
             pass
-        raise error.RepoError(_("unknown revision '%s'") % key)
+        raise error.RepoLookupError(_("unknown revision '%s'") % key)
 
     def local(self):
         return True