First pass at separating storage from computation

Pipeline node now does not allocate. That's handled by the new
Allocate node. Chunk now takes a pair of dimensions - the level
to store at and the level to compute at:

buffer_t's now separately track size and strides. They also can
express min, which defines what function index is meant by the
first element of the buffer.

Outstanding bugs:
ptx is broken
dense loads are broken because innermost stride is unknown

To do before this is useful performance-wise:
Only compute the new values that are needed when you're inside
a serial for loop. I.e. do a rectangle exclusion of the stuff
computed on all previous iterations.
Merge branch 'master' into split-store-compute
bilateral grid uses relative path to llvm and no new C++ features
py bindings -- add bilateral grid example
Fixed a allocation size bug

We were computing allocations based on extent required instead
of extent computed
py bindings -- first stab at making autotune work on bilagrid
Remove accidental status spew
Add uniform, image support to Rehydrate
Capture major note in PTX host implementation

The method of injecting buffer dirty marks along Pipeline boundaries 
no longer should work with schedule/storage separation, but it's not
clear it was ever sufficiently complete.
Merge branch 'master' of github.com:halide/Halide
py bindings -- do not use exp time algo for enumerating valid schedules
Merge branch 'master' of https://github.com/halide/Halide
Fix rehydration for uniforms, images

The rehydrate test is now more thorough.
Merge branch 'master' of github.com:halide/Halide
py bindings -- include Halide.h
Merge branch 'master' of https://github.com/halide/Halide
py bindings -- unfinished camera_pipe port, fix camera_pipe Makefile to use rel paths to llc/opt
camera pipe -- clamp to allow it to compile
Testing serialization of camera_pipe

This required fixing the hack used to make processed iterate over a bounded
color loop, since deserialization can't cope with RHS vars which aren't in the
LHS args.
Switch swig interface to include the full Halide.h