Upgrade PugiXML and force it to be strictly inline.

The upgrade is necessary for more modern C++ compilers/libs (I ran into
it with clang when using libc++).

The inline forcing, I hope, prevents us from needing to worry about about
conflicting linkage or namespaces.
One more Pugi upgrade change
Re-establish OIIO wrapper namespace around pugi
Update builtinplugins.tex (typo fix)
Allow more slop in the timer_test (tolerance of 1/100s instead of 1/1000s).

For some reason, this test fails on OS 10.9 Mavericks, seemingly because
there's a bit more slop in how long a usleep() really takes to wake you
up again.  It used to be within 1/1000s, but sometimes it's a bit more
on this OS.  Changing the tolerance to 1/100s makes the tests pass, and
I don't see any problem with it.

I've read that one of Mavericks' major design goals was to improve
power efficiency, and apparently the process scheduler tries very hard
to juggle time slices around to make slices abut (to amortize the power
efficiency of the Intel chips, which have to ramp up and down a bit when
there's processor activity).  It wouldn't surprise me if this ends up
making usleep just a bit less consistent in precisely how long it will
be before the process wakes up again.  How's that for a hypothesis?
More robust clang detection
Make tbb compilation safe for libc++
Better hints to find openjpeg
OpenEXR deep image fixes -- must rename or suppress some attributes
whose careless copying from one file to another will cause problems.