filemerge: reduce some duplication in `_maketempfiles()`
The two callers of the local `maketempfrompath()` function used the
returned file object in the same way. We can reduce duplication by
moving that code into the function.
Differential Revision: https://phab.mercurial-scm.org/D12192
@echo off
powershell -NoProfile -ExecutionPolicy unrestricted -Command "& '%~dp0\editmergeps.ps1' %*"