oslibs, codecs (macosx, windows): recompile libmodplug with several
fixes included, and midi formats, gus patches, and wav formats loading
disabled.


git-svn-id: http://svn.code.sf.net/p/quakespasm/code/trunk/quakespasm@936 af15c1b1-3010-417e-b628-4374ebc0bcbd
oslibs, codecs (macosx, windows): update mikmod.h from mainstream.


git-svn-id: http://svn.code.sf.net/p/quakespasm/code/trunk/quakespasm@937 af15c1b1-3010-417e-b628-4374ebc0bcbd
net_sys.h: update from uhexen2

git-svn-id: http://svn.code.sf.net/p/quakespasm/code/trunk/quakespasm@938 af15c1b1-3010-417e-b628-4374ebc0bcbd
Add lowpass filter
switch to fir filter