hgweb: show correct error message for i18n environment

If exception is error.LookupError and running in i18n environment,
below condition is always true.
Because msg is translated and dosen't contain 'manifest'.

    if util.safehasattr(err, 'name') and 'manifest' not in msg:

This patch creates a new exception class and uses it instead of
string match.

mercurial/context.py

@@ -291,7 +291,7 b' class changectx(object):'
             try:
                 return self._manifest[path], self._manifest.flags(path)
             except KeyError:
-                raise error.LookupError(self._node, path,
+                raise error.ManifestLookupError(self._node, path,
                                         _('not found in manifest'))
         if '_manifestdelta' in self.__dict__ or path in self.files():
             if path in self._manifestdelta:
@@ -299,7 +299,7 b' class changectx(object):'
                         self._manifestdelta.flags(path))
         node, flag = self._repo.manifest.find(self._changeset[0], path)
         if not node:
-            raise error.LookupError(self._node, path,
+            raise error.ManifestLookupError(self._node, path,
                                     _('not found in manifest'))
 
         return node, flag

mercurial/error.py

@@ -27,6 +27,9 b' class LookupError(RevlogError, KeyError)'
     def __str__(self):
         return RevlogError.__str__(self)
 
+class ManifestLookupError(LookupError):
+    pass
+
 class CommandError(Exception):
     """Exception raised on errors in parsing the command line."""
 

mercurial/hgweb/hgweb_mod.py

@@ -245,7 +245,8 b' class hgweb(object):'
         except (error.LookupError, error.RepoLookupError), err:
             req.respond(HTTP_NOT_FOUND, ctype)
             msg = str(err)
-            if util.safehasattr(err, 'name') and 'manifest' not in msg:
+            if (util.safehasattr(err, 'name') and
+                not isinstance(err,  error.ManifestLookupError)):
                 msg = 'revision not found: %s' % err.name
             return tmpl('error', error=msg)
         except (error.RepoError, error.RevlogError), inst: