JK2 version is now a separate executable, openjo_sp.
JK2 renderer is now separate, rdjosp-vanilla.
Changed __NO_JK2 to JK2_MODE (negated).
jk2game renamed to jospgame since we're not binary compatible anyway.
com_jk2 defaults to 1 in JK2 mode.
Added option to not build renderers.
Got rid of com_jk2 since that's a separate executable now.
Merge pull request #506 from mrwonko/jk2-clean

JK2 support in separate executable/library; option to compile renderers