tests: use $HTTP_DATE$ for Date header
Support for the $HTTP_DATE$ substitution was recently added. Let's
adopt it more widely.
We had to tweak the substitution to be case insensitive, since
HTTP headers are case insensitive. I also found a minor test
issue not globbing over the length of the Server response header.
Differential Revision: https://phab.mercurial-scm.org/D2839
#require serve killdaemons
$ hg clone http://localhost:$HGPORT/ copy
abort: * (glob)
[255]
$ test -d copy
[1]
$ $PYTHON "$TESTDIR/dumbhttp.py" -p $HGPORT --pid dumb.pid
$ cat dumb.pid >> $DAEMON_PIDS
$ hg clone http://localhost:$HGPORT/foo copy2
abort: HTTP Error 404: * (glob)
[255]
$ killdaemons.py