contrib/packaging/requirements.txt.in

hgweb: unbyteify the 100-continue check

The environment seems to be `str` or `tuple[int]`, and the same check in
`wsgicgi.py` is already `str` based, so I suspect this was wrong.  I think what
happened here is that the string wasn't `r''` prefixed in 482d6f6dba91 like
`wsgicgi.py`, so it got wrongly byteified in 687b865b95ad when converting to
byte literals en masse.

# Declare requirements for generating the compiled (frozen)
# set of requirements in ./requirements.txt.

docutils
jinja2