Use named variable for LuaRef in equipSet callback setting

This works around a bug happening on Mac OS X (and perhaps clang as
well). (Closes #2993)
Check the stack size when trying to call a Lua{Object, Table} method

(Closes #3000)
Add a bunch of LUA_DEBUG_START guards
Avoid some Lua stack leaks in the UI code.

(Closes #3000)
(Closes #3001)
(Closes #2999)
(Closes #2997)
(Closes #2996)
add readout of Lua stack size to debug info overlay
Merge remote-tracking branch 'laarmen/checkstack_callmethod'
Merge remote-tracking branch 'laarmen/leaky_ui'
Merge remote-tracking branch 'laarmen/fix_2993'
whitespace in changelog