Python bindings for ImageBufAlgo

The vast majority of ImageBufAlgo functions are hereby exposed to Python.

A small number of functions have temporarily been omitted.  These are
all rarely used, and had call signatures where I was unsure of the
correct Pythonic way to organize them.  We'll come back to this later,
but in the mean time, we have now working versions of almost everything
else in ImageBufAlgo that you can use from Python.
Rebuild PDF docs
Re-establish OIIO wrapper namespace around pugi
More robust clang detection
Make tbb compilation safe for libc++
Replace vector with scoped_array for better performance (no needless fill)
OpenEXR deep image fixes -- must rename or suppress some attributes
whose careless copying from one file to another will cause problems.
ImageBufAlgo::flatten() and 'oiiotool --flatten'
turn deep images into flat images by depth-compositing the samples
within each pixel.
Better hints to find openjpeg
Better reference match for newer certain versionf of libgif
FITS: try to be sensible for 1-D images
CHANGES update
Fix iv broken on Mavericks and other platforms where GLU is deprecated.
Simplify HDF5 finding, also makes it work on Mavericks
Turn Field3D console output off if it's new enough to support setVerbosity
SPI specific fixes for OSX compilation
Refactored action_ociolook to use ImageBufAlgo::ociolook instead of building a  ColorProcessor and passing it to ImageBufAlgo::colorconvert.
Update Tinyformat to the latest release
Scan for matching frames if no explicit framespec is provided.

Fixes #713.
SPI specific -- upgrade our locked Field3D version, now that bugs are fixed