Fixed screen twitches with "shakes" sound shader

Caused by inaccuracies in the precached amplitude data in the OpenAL
backend, see https://github.com/dhewm/dhewm3/pull/71 for more details.

Video sample (not mine):
http://www.youtube.com/watch?v=ZUohifAbPW0
The "twitches" can also be observed right at the beginning of the
mars_city2 map.
Use updated minizip version for unzip

The implementation is now in framework/minizip/*
instead of framework/Unzip.cpp

This was version 0.15beta, now we use 1.1 from
zlib 1.2.7/contrib/minizip

Some code had to be adjusted for this, but it got
cleaner on the way
Replace custom unzip functions with standard ones

unz[SG]etCurrentFileInfoPosition() isn't needed anymore,
because newer minizip versions have unz[SG]etOffset() for
that purpose.
Merge pull request #58 from DanielGibson/update-zip

Update zip implementation from minizip 0.15 to minizip 1.1
Should also bring (untested) zip64 support for zip files >2GB.
Minor spelling fix.
Merge pull request #73 from rohitnirmal/spelling

Minor spelling fix.
SDL2 support fix
Enable loading of original DOOM 3 save games.

This makes it possible to use dhwem3 as a drop-in replacement for an existing doom3 installation.
Merge pull request #75 from hurikhan/SDL2

Fix compilation with SDL2 release
fixed potential bug.
Merge pull request #86 from dotfloat/master

fixed nested for-loops using the same counter variable in d3xp's idWeapon::GetAmmoNameForNum
Fix compilation on Gentoo

For some reason Gentoo renamed zlibs OF() macro to _Z_OF
Our minizip uses OF(), so add a #define for it in case
_Z_OF is defined.

Thanks to salamanderrake for the fix
Merge pull request #76 from bk138/master

Enable loading of original DOOM 3 save games (by accepting the original game name "DOOM 3"
Fix building with Gentoo's patched zlib.
Merge pull request #88 from waldheinz/drop-minizip-of-usage

Fix building on Gentoo by providing OF() macro if necessary

.. I hope this time it works for everyone.