repoview: add a FilteredIndexError class

This exception is a more precise IndexError that will allow us to
issue a special message when we end up accessing a filtered revision.

mercurial/changelog.py

@@ -196,25 +196,25 b' class changelog(revlog.revlog):'
     def node(self, rev):
         """filtered version of revlog.node"""
         if rev in self.filteredrevs:
-            raise IndexError(rev)
+            raise error.FilteredIndexError(rev)
         return super(changelog, self).node(rev)
 
     def linkrev(self, rev):
         """filtered version of revlog.linkrev"""
         if rev in self.filteredrevs:
-            raise IndexError(rev)
+            raise error.FilteredIndexError(rev)
         return super(changelog, self).linkrev(rev)
 
     def parentrevs(self, rev):
         """filtered version of revlog.parentrevs"""
         if rev in self.filteredrevs:
-            raise IndexError(rev)
+            raise error.FilteredIndexError(rev)
         return super(changelog, self).parentrevs(rev)
 
     def flags(self, rev):
         """filtered version of revlog.flags"""
         if rev in self.filteredrevs:
-            raise IndexError(rev)
+            raise error.FilteredIndexError(rev)
         return super(changelog, self).flags(rev)
 
     def delayupdate(self):

mercurial/error.py

@@ -16,6 +16,9 b' imports.'
 class RevlogError(Exception):
     pass
 
+class FilteredIndexError(IndexError):
+    pass
+
 class LookupError(RevlogError, KeyError):
     def __init__(self, name, index, message):
         self.name = name