If bytecode is requested and fails to load, load original file
instead. Force re-write of bytecode if that succeeds.
This is useful if there is bytecode newer than the source file that
the current Lua version can't load, for example when migrating from
LuaJIT 2.0 to 2.1, which changed bytecode format.
Fixes confusing cases such as in T2728.
The API (that didn't work in the first place) was used wrongly
as it was assumed its behaviour was the same as mkstemp (duh!).
It turns out eina's version doesn't replace the input string but
returns a tmpstr instead.
@fix