contrib: make editmergeps use -NoNewWindow option in Start-Process cmdlet
Running 'Start-Process -Wait "vim" "+10" "filename"' from PowerShell
actually spawns a separate cmd window to run vim in. This looks ugly
and in most cases not what user wants. During my initial testing I was
using the Cmder app, which made me not notice this (it captures new
windows as new tabs).
Our full contribution guidelines are in our wiki, please see:
https://www.mercurial-scm.org/wiki/ContributingChanges
If you just want a checklist to follow, you can go straight to
https://www.mercurial-scm.org/wiki/ContributingChanges#Submission_checklist
If you can't run the entire testsuite for some reason (it can be
difficult on Windows), please at least run `contrib/check-code.py` on
any files you've modified and run `python contrib/check-commit` on any
commits you've made (for example, `python contrib/check-commit
273ce12ad8f1` will report some style violations on a very old commit).