Instead of using a hardcoded or default path to the perl file the .bat
file is a wrapper for, we use a path that means the file is found in
the same directory as the .bat file.
Patch by Anton Voloshin, slightly tweaked by me.
Backpatch to all live branches
Discussion: https://postgr.es/m/2b7a674b-5fb0-d264-75ef-ecc7a31e54f8@postgrespro.ru
Build.bat and vcregress.bat got similar treatment years ago. I'm not sure
why install.bat wasn't treated at the same time, but it seems like a good
idea anyway.
The immediate problem with the old install.bat was that it had quoting
issues, and wouldn't work if the target directory's name contained spaces.
This fixes that problem.
Andrew Dunstan
Heikki Linnakangas
Peter Eisentraut
Magnus Hagander