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
https://bz.mercurial-scm.org/1089
$ hg init
$ mkdir a
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ hg ci -m m a
$ mkdir a b
$ echo a > a/b
$ hg ci -Am m
adding a/b
$ hg rm a
removing a/b
$ cd b
Relative delete:
$ hg ci -m m ../a
$ cd ..