Tell gcc/clang to ignore the fact that math functions can set errno (helps codegen of sqrtf in particular)
Fix thread contention issue in testshade.

We were doing something incredibly stupid in testshade --
setup_shaderglobals was setting sg.renderstate by asking for
shadingsys->raytype_bit(ustring(raytype)) for EVERY shade, instead of
finding out which bit it was once and using that int all the time.

Most egregiously, the construction of a ustring was creating thread
contention (it was the SAME ustring every time, which is the worst case
for the locking in the ustring table -- at least if they were different
character sequences, the ustring internals are unlikely to have them
vying for the same lock!).

The net result was that for small shaders especially, the
setup_shaderglobals thread contention could dominated runtime when more
than a few threads were running. This made testshade very unreliable for
benchmarking the actual execution time of short shaders when many
threads were used. Ick!

The fix is very simple, just ask for the bit once globally, and use that
result when setting up the SG's for the individual shades.
Build scripts minor reformatting and better help messages.
* Rearrange Makefile wrapper so that 'make help' is much more readable.
* Added USE_CPP11, USE_LIBCPLUSPLUS, and EXTRA_CPP_ARGS (copied from
  OIIO's build scripts).
* Some minor reformatting and movement to make it align to similar constructs
  in the OIIO Makefile and CMakeLists.txt (makes it easier to diff and port
  improvements in the build system from one project to another).
testsuite/test-derivs -- test for correct texture derivatives
Add faster, lower precision variants of the standard math routines. These are enabled by default

The system math library can be reverted to with USE_FAST_MATH=0
Make it build on llvm 3.5
Fix signed/unsigned comparisons
testsuite ref output changes after recent transcendantal approximations
More testsuite reference output updates
Another round of careful updates to testsuite reference output.
At this point, both OSX and Linux pass 100% of tests for me!
CHANGES
bump dev release version
RendererServices API overhaul -- all the texture functions have been
slightly changed to explicitly pass nchannels and the derivative pointers
rather than embedding those in the TextureOpt struct. This goes along with
an OIIO-side change that altered the TextureSystem API in a similar way and
eliminated those fields from TextureOpt. This was part of a big overhaul
aimed at SSE-izing the TextureSystem internals.
OSL-side changes corresponding to SIMD overhaul of TextureSystem.

TextureSystem has eliminated the nchannels and derivs field from
TextureOpt, instead passing those explicitly to the texture API functions.
We change here to match. Also, we make use of the new OIIO::simd::float4
class, to exploit SSE and other instruction-level SIMD in the glue code
surrounding the texture calls.
simd Make/cmake
Bump SPI minimal SSE level to 4.1 on spinux, 4.2 on OSX
Merge pull request #410 from lgritz/lg-simd

Use SIMD in texture system
Remove fastmath.h, now that the same functionality is in OpenImageIO/fmath.h
Make sure SIMD flags are propagated to compilation of llvm_ops.cpp
Update tests after recent fmath changes - erf etc