"loop" and "uninterruptible" in MugShot definitions

[Turret49]

Currently you can set a mug shot state to last indefinitely (until another state is set) by setting a frame's tics to -1, but the only way to achieve an animated looping mug shot state is by the idle state, or doing a lot of scripted SetMugShotState or SBARINFO drawimage hackery that easily breaks.
An example of a custom looping mugshot state would be a state where the player character is talking, and you want the animation to play until a desired time. A "loop" flag or loop keyword a la DECORATE would help for this.

An "uninterruptible" (except by death) flag would be useful, too. The "Pain" state cancels/disables other states as long as the player's screen is red, and if you use the disablepain flag, the pain state will no longer show directional damage if it's jumped to manually.