convert: better feedback when filtering out empty revisions

Original patch by Herbert Griebel <[e-mail]>

hgext/convert/hg.py

@@ -155,6 +155,7 b' class mercurial_sink(converter_sink):'
             man = self.repo.manifest
             mnode = self.repo.changelog.read(bin(p2))[0]
             if not man.cmp(m1node, man.revision(mnode)):
+                self.ui.status(_("filtering out empty revision\n"))
                 self.repo.rollback()
                 return parent
         return p2

tests/test-convert-cvs-builtincvsps.out

@@ -42,6 +42,7 b' sorting...'
 converting...
 2 Initial revision
 1 import
+filtering out empty revision
 rolling back last transaction
 0 ci0
 updating tags

tests/test-convert-cvs.out

@@ -34,6 +34,7 b' sorting...'
 converting...
 2 Initial revision
 1 import
+filtering out empty revision
 rolling back last transaction
 0 ci0
 updating tags