D5227: pycompat: adding Linux detection and fixing Mac

[Joerg Sonnenberger]

On Tue, Nov 06, 2018 at 03:54:20AM +0000, rdamazio (Rodrigo Damazio Bovendorp) wrote:
> REVISION SUMMARY
>   Python 3 recommends detecting OSs with the prefix of the platform, but we were
>   comparing the full string for macOS. We also didn't have Linux detection, which
>   is convenient for extensions to use (rather than have some OSs detected by hg
>   and some by the extension).

I'm actually quite against islinux. What reasons should *any* code have
to test specifically for Linux and not a platform feature?

Joerg