Fix loading of lumps from directory on OS X

Use POSIX-compliant opendir() / readdir() functions instead fts_open() / fts_read()
Unlike Linux version, on OS X fts_read() inserts extra slash character between source directory and traversed entry paths
Added GetActorPowerupTics ACS function
Merge branch 'master' of https://github.com/Edward850/zdoom
More editing flags

PSX-inspired flags to change the render styles of monsters (and other
things).
Less flags, more generic properties
Updated documentation
CANRAISE state definition

CANRAISE state for allowing a monster to be resurrected without an
infinite frame
Merge branch 'master' of https://github.com/rheit/zdoom
Merge branch 'master' of https://github.com/Edward850/zdoom
Merge branch 'master' of https://github.com/rheit/zdoom
- fixed typo in xlat files (they don't use exactly C syntax.)
Init new non-0 fields for non-UDMF maps.
Hexen too.
Hexen also needs to init 0 fields.
Typo.
Merge branch 'master' of https://github.com/Gaerzi/zdoom
Merge branch 'master' of https://github.com/rheit/zdoom
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.