tests: test that the pid returned by `hg serve` looks reasonable
This failed on windows before win32.spawndetached has been fixed. The process
name was "cmd.exe" and not "hg.exe" or "python.exe".
Minimal hgk check
$ echo "[extensions]" >> $HGRCPATH
$ echo "hgk=" >> $HGRCPATH
$ hg init repo
$ cd repo
$ echo a > a
$ hg ci -Am adda
adding a
$ hg debug-cat-file commit 0
tree a0c8bcbbb45c
parent 000000000000
author test 0 0
revision 0
branch default
phase draft
adda
$ cd ..