add python bindings (still have swig errors)
fix bugs in py bindings
builds but has problems still
Check both ends when producing a condition for clamped vector load
Performance improvement for clamped vector load.

Now only checks necessary conditions in the case where stride
is a known const.

Also added correctness testing in test case.
More reliably link libpng for tutorials
Made the clamped vector load test less strict

To cope with the performance noise you get from running the
tests at -j > 1
Added build instructions for lessons on os x
Merge branch 'master' of github.com:halide/Halide
Fix a typo in function naming.
Vectorized calls to externs work again.
Merge branch 'master' of github.com:halide/Halide
Added two more lessons
Type-based alias analysis actually works now

Turns out the types had to have the same root node to be compared.
Don't lift cast nodes out into let statements

It breaks peephole matching that assumes cast nodes will be in place.
Expose the remove_lets method from CSE

May be useful as a prepass to peephole matching during codegen.
fix more bugs in py bindings
remove prototypes that are never defined from Bounds.h (bounds_of_expr() and Interval::Interval())
Merge branch 'master' into python
commit the right files for python binding