Previously took only the filename, so the directory
component was stripped. This broke dependencies for
basically every file.

P_ZMovement: add a P_MobjWasRemoved check after P_CheckPosition, so we can bail out if the mobj was removed (by Lua most likely)

This was done by storing flag-for-removal status as a boolean inside the player struct.
Bot players are instead removed at the start of G_Ticker, rather than being removed immediately by G_RemovePlayer.

Bugfix - Fix sporadically occurring incorrect userdata types in Lua, caused by previously loaded userdata which didn't get invalidated in previous sessions.

Invalidate userdata for line and mapthing args.
Invalidate userdata for slopes and their normal, origin and direction vectors.

(Demos do not call CL_Reset BTW.)

And quote variable name.

According to this answer--
https://stackoverflow.com/a/45952425
--Make will always prefer a unix shell, even on Windows,
if one can be found in Path. So we can't check PATH to
determine if it's a Windows shell... this is just too much
bother.

If a variable is defined as in 'make CC=gcc-10', then that
definition overrides anything other definition in the
Makefile.

After a checkout from before revision, old directories
such as bin/Linux64 only remain if untracked files exist
within. This may be confusing to the user. They may even
use an outdated executable if it is one of those untracked
files.

This is for MSYS2, which requires unix shell commands.

File function is not supported < Make 4.2.

With added textual contrast.