contrib/editmergeps.bat

tests: conditionalize color output on abort

This broke in afc4ad706f9c.  I'm not sure why other aborts don't need to be
conditionalized, but `hg help foo` does abort in red for both msys and cmd.exe.

@echo off
powershell -NoProfile -ExecutionPolicy unrestricted -Command "& '%~dp0\editmergeps.ps1' %*"