Added slow monsters, the inverse of fast monsters

This is a skill setting only, no "always slow" or "never slow" actor
flags, and no DM flags.
Added slow monsters to Strife's easiest skill
- check +logfile explicitly at the start of execution. Due to the custom CVAR rewrite it would get called so late that it'd miss half of the log.
- added version check for Windows 8. I also would have liked to add 8.1 but due to some incredibly stupid changes in the version API it's no longer possible to reliably retrieve the correct Windows version for later builds.
Merge branch 'master' of https://github.com/rheit/zdoom
Fixed P_LookForPlayers scanning redundancies

- Players could be scanned multiple times, repeating expensive tests
- Players could be skipped completely and become invisible as a result
Invisibility would could P_LookForPlayers early
Merge branch 'master' of https://github.com/Edward850/zdoom
Added slow states to relevant Strife monsters

Namely, acolyte, shadow acolyte, reaver, stalker, and turret. Info on
which states needed the slow flag was obtained with Quasar's permission
by looking at G_InitNew() in g_game.c and the info.c state tables from
Chocolate Strife.
Also added fast flag to acolyte states that needed it, based on the same
source.
Merge branch 'slowstate' of https://github.com/Gaerzi/zdoom
Merge branch 'master' of https://github.com/rheit/zdoom
Merge branch 'master' of https://github.com/coelckers/gzdoom