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.
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
Fixed initialization of Hexen-style things

Recently added pitch and roll members were not initialized with zeroes when loading Hexen-style maps
At least, hitscan attack can be fired in random direction because of this
Add shadow and subtract styles to ACS.

There is a matching pull request for rheit/acs.
Restore shadow renderstyle.

It was accidentally lost in r3085.
Merge branch 'master' of https://github.com/Gaerzi/zdoom
Fixed crash on attempt to load corrupted data file

Instance of FileReader is no longer destructed when header of data file is valid but complete loading of file fails
Loading of truncated .zip file is the simplest test case
Added simple check for unsupported compression method in .7z files
Added support for LZMA2 compression method in .7z archives

Updated LZMA SDK to version 9.20
http://www.7-zip.org/sdk.html
http://downloads.sourceforge.net/sevenzip/lzma920.tar.bz2
- added constants for sound channels 5-7.
Fixed file list in VS2005 project of LZMA library
Fixed compilation with updated LZMA library using Visual Studio
Merge branch 'master' of https://github.com/rheit/zdoom into lzma2
Added static RNGseed control