Lua: hud.enabled and v.getLocalTransFlag()

Adds simple Lua functions that can probably go a long way... more or less:

• hud.enabled(huditem) will return true or false depending on if huditem is enabled or disabled, which will DEFINITELY help mods using huds not look out of place when another mod decides to disable huds for misc purposes.
• v.getLocalTransFlag() is a way more situational, it returns V_HUDTRANS as a regular V_xxTRANS flag, which means that people can work from that transparency to get consistent results with the player's settings.