Add LZMA_RET_INTERNAL1..8 to lzma_ret and use one for LZMA_TIMED_OUT.

Add LZMA_RET_INTERNAL1..8 to lzma_ret and use one for LZMA_TIMED_OUT.

LZMA_TIMED_OUT is *internally* used as a value for lzma_ret
enumeration. Previously it was #defined to 32 and cast to lzma_ret.
That way it wasn't visible in the public API, but this was hackish.

Now the public API has eight LZMA_RET_INTERNALx members and
LZMA_TIMED_OUT is #defined to LZMA_RET_INTERNAL1. This way
the code is cleaner overall although the public API has a few
extra mysterious enum members.