- Remove a duplicate of a custom offsetof macro.

It's already defined in cmdlib.h .
Animate switches when bumped
- added jpalomo's submission to make freelook a 3-state setting, like crouch and jump. This required moving around the flags a bit so demo compatibility had to be bumped. It may also require adjustment for launchers that can set the dmflags.
Merge branch 'master' of https://github.com/rheit/zdoom
Merge branch 'redundant_offsetof_macro' of https://github.com/edward-san/zdoom
Merge branch 'upstream' of https://github.com/Edward850/zdoom
- changed handling of DF_NO_COOP_WEAPON_SPAWN dmflag so that weapons are not determined by class type but by a newly added flag WEAPONSPAWN, to allow CustomInventory replacements to act like weapons when being spawned.