Bug:1201 hg convert on CVS working copy produces Traceback

Fix identified by [e-mail]

Changed usage fron os.environ["HOME"] to expanduser("~/.cvspass") as
this is the
 only usage of this construct in mercurial sources.

hgext/convert/cvs.py

@@ -161,7 +161,7 b' class convert_cvs(converter_source):'
 
                 if not passw:
                     passw = "A"
-                    pf = open(os.path.join(os.environ["HOME"], ".cvspass"))
+                    pf = open(os.path.expanduser("~/.cvspass"))
                     for line in pf.read().splitlines():
                         part1, part2 = line.split(' ', 1)
                         if part1 == '/1':