changectx: wrap the `changeid` processing in a try/except

We are going to introduce more precise exception classes for filtered nodes. So
we will have to upgrade them to the `RepoLookupError` level here. We wrap the
whole thing into a try/except to ease this future catching. Some of the current
exception catching will be moved in this one. But the current changeset focuses
on code movement only.

mercurial/context.py

@@ -376,6 +376,7 b' class changectx(basectx):'
             changeid = '.'
         self._repo = repo
 
+        try:
         if isinstance(changeid, int):
             try:
                 self._node = repo.changelog.node(changeid)
@@ -452,16 +453,18 b' class changectx(basectx):'
         # lookup failed
         # check if it might have come from damaged dirstate
         #
-        # XXX we could avoid the unfiltered if we had a recognizable exception
-        # for filtered changeset access
+            # XXX we could avoid the unfiltered if we had a recognizable
+            # exception for filtered changeset access
         if changeid in repo.unfiltered().dirstate.parents():
-            raise error.Abort(_("working directory has unknown parent '%s'!")
-                              % short(changeid))
+                msg = _("working directory has unknown parent '%s'!")
+                raise error.Abort(msg % short(changeid))
         try:
             if len(changeid) == 20:
                 changeid = hex(changeid)
         except TypeError:
             pass
+        except Exception:
+            raise
         raise error.RepoLookupError(
             _("unknown revision '%s'") % changeid)