Use luaL_loadbufferx and luaL_loadfilex instead, being explicit about
whether to accept binary chunks.

Added compiler option LUA_NODEBUGLIB to make Lua with no open debug
library + small improvements in the manual.

'lua_load' does not preserve the stack through the calls to the
reader function, as it should. Immediately after the first call (to
detect whether chunk is binary) it adds stuff, and it also adds a new
table when starting the compilation of each new function.

OP_VARARGPREP neither sets nor uses L->top.

In function 'funcargs', some compilers can complain that 'args' can be
used unitialized, due to the default case (syntax error).