debugdownload: read repository hgrc if there is one
The command does not require a repository, but will use it if there is one.
This simplifies the reading of the remote destination when testing for
largefile based url.
$ hg init
$ echo This is file a1 > a
$ hg add a
$ hg commit -m "commit #0"
$ ls
a
$ echo This is file b1 > b
$ hg add b
$ hg commit -m "commit #1"
$ hg co 0
0 files updated, 0 files merged, 1 files removed, 0 files unresolved
B should disappear
$ ls
a