Handle calls with max. args in backends even after SPLIT.
FFI: Improve error messages for arithmetic and comparison operators.
FFI: Insert no-op type conversion for pointer to integer cast.
FFI: Fix unroll limit for ffi.fill().
FFI: Must sink XBAR together with XSTOREs.
Add missing PHI barrier to string.sub(str, a, b) == kstr FOLD rule.
Fix compatibility issues with Illumos.

Thanks to Theo Schlossnagle.
Merge branch 'master' of luajit-2.0