Simplification of localization.

[- <far-far@...>]

Lua 5.3 is coming.
It very necessary to move all C strings from all source files of Lua 5.3 to one header file.
It will make possible to translate error messages to other languages in a simple way (by replacing that file).

For example. 
File lmsg.h


// from lapi.c
#define MSG_UNACCEPTABLE_INDEX    "unacceptable index"
#define MSG_INVALID_INDEX                      "invalid index"
#define MSG_UPVALUE_TOO_LARGE      "upvalue index too large"

// from lauxlib.c
......

// from lauxlib.c
...