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'"
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..