[Dev-luatex] Snapshot update

[Taco Hoekwater]

Hi,

The upload of a new snapshot will be finished in a few moments.
This is a bugfix only, no new features, but I wanted to get this
out of the way quickly.

The list of fixed bugs/problems:

* Previously, including \the inside and argument to \directlua could
   result in crashes and failures (due to \the changing a key variable)

* texio.write() failed to clean up correctly so that the string pool
   became corrupted

* The lua package.path contained backslashes on windows, but that doesnt
   work because lua interpreted them als string escapes

* Assigning large values to one of the tex.toks[] registers could fill
   up main_memory because the memory was never cleared

* tex.toks[], tex.count[] and tex.dimen[] assignments did not respect
   grouping

* \directlua containing empty lines made the lua interpreter crash
   because of auto-generated \par tokens.

* \string created non-utf-8 output

* Bare bytes with values 0x80-0xBF in the input went unnoticed.
   This now raises an utf-8 encoding error

* startup.lua is now searched for by the C code instead of lua
   'require'. This eliminates the warning message if it cannot be
   found. The search path has also changed slightly: Only the
   current directory and the internal equivalent of
      'kpsewhich --format=texmfscripts'
   are tried.

Cheers, Taco