-Refactor PTR_ShootTraverse and move the line collision related code into a new function, P_ShootLine.
-Fix collisions with 'sky wall hack' lines when co_fixweaponimpacts is enabled.
-Add emulation for lines flagged with ML_TWOSIDED and no backsector.

git-svn-id: http://odamex.net/svn/root/trunk@3837 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Fix missile collisions with 'sky wall hack' lines when co_fixweaponimpacts is enabled.

git-svn-id: http://odamex.net/svn/root/trunk@3838 b0bcef46-2027-0410-bd56-ab726e9a1d04
-Add an abstraction for the two gamma correction types in v_gamma.h.
-We no longer need to have vanilla gamma level offset by 1 to maintain compatibility with ZDoom. Vanilla gamma now ranges from 0.0 - 7.0.
-Changed ZDoom gamma levels to range from 0.5 - 3.0 with 0.1 increments from bumpgamma.

git-svn-id: http://odamex.net/svn/root/trunk@3839 b0bcef46-2027-0410-bd56-ab726e9a1d04