testlib: move the prune alias into a shell script for Windows
Cramming all of this directly into an alias doesn't play nicely on Windows.
Various test-exchange-obsmarkers-case-XX.t were failing with:
abort: cannot select revision when creating marker
It turned out that inside debugcommands.debugobsolete(), the following differed
from Linux (where they were empty, at least in the case I debugged):
'rev': ['.`;'],
'template': "'{node}\\n'"
#if no-windows no-osx
$ mkdir -p xdgconf/hg
$ echo '[ui]' > xdgconf/hg/hgrc
$ echo 'username = foobar' >> xdgconf/hg/hgrc
$ XDG_CONFIG_HOME="`pwd`/xdgconf" ; export XDG_CONFIG_HOME
$ unset HGRCPATH
$ hg config ui.username
foobar
#endif