Clamp negative rev numbers at zero.
Prior to this change, trying to run "hg log -r -50:" in a repo with
less than 50 changes caused an error. Now that we clamp at zero: no
more error.
#!/usr/bin/env python
#
# An example CGI script to use hgweb, edit as necessary
import cgitb, os, sys
cgitb.enable()
# sys.path.insert(0, "/path/to/python/lib") # if not a system-wide install
from mercurial import hgweb
h = hgweb.hgweb("/path/to/repo", "repository name")
h.run()