Makefile.PL: Add Inline::C dependency

Inline::C is no longer shipped with Inline.
t/234-layout-restore-output: Remove unused import

List::MoreUtils is imported but not used.
Use command -v (built-in) instead of which(1) (Thanks val)

fixes #1380
set DesktopNames (which gdm uses) (Thanks Yves-Alexis)