procutil: use unbuffered stdout on Windows
Windows doesn't support line buffering, treating it as fully buffered. This
causes output of slow commands to stutter. We use unbuffered instead.
Welcome to Mercurial for Windows!
---------------------------------
For configuration and usage directions, please read the ReadMe.html
file that comes with this package.
Also check the release notes at:
https://mercurial-scm.org/wiki/WhatsNew