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'"