lua_pushunsigned undocumented

[Rapin Patrick <rapin.patrick@...>]

Lua 5.2 introduced the new type lua_Unsigned for bit operations, and 
along it a number of API functions like lua_tounsigned or 
luaL_checkunsigned.
I noticed recently that although the function 
lua_pushunsigned is logically declared in lua.h, defined in lapi.c and 
heavily used in lbitlib.c, there is no mention of it in the 
documentation. It seems to have been forgotten.