Merge pull request #300 from Nazg-Gul/dev

Fix some meory leaks in adaptive evaluator
glViewer: use GL timer query to measure the GPU draw timing more precisely.
examples: use GL timer query to measure the GPU draw timing more precisely.
Decrease compiler warning thresholds and fix outstanding warnings.

Note: this round fixes clang / gcc -Wetra warnings. More fixing remains for icc -w3 errors.
Adding a programmable image shader to gl_hud

- add a framebuffer to gl_hud with programmable image shader
- add optional SSAO image shader to the new framebuffer
- add screenshot to png functionality
- implement in glViewer

note: ptexViewer and some others still need refactoring to use the new hud capabilities
Decrease compiler warning thresholds and fix outstanding warnings (continued)

- turn off some of icc's remarks (mostly because of tbb)
- fix many of icc -w3 remarks (more to fix once i can work around icc 14.0 linker barfing)
Minor fixes to gl_hud and gl_framebuffer

- leave framebuffer off by default (and remove SSAO UI from examples)
- fix some resources leakage when toggling SSAO on/off
Fix framebuffer shader compiling for OSX

The driver apparently does not tolerate #version after a #define
Fix compiler warnings in OsdClVertexBuffer
Fix icc build problems

- icc asserts out because of the length of rpath, so we are temporarily removing the elements
  that aren't defined until chrpath is invoked by cmake (this means installed executables are
  missing paths to the built OSD dsos)
- comment out some of the warnings for missing packages if they were deliberately turned off
Add command line option to CMake's options

It solves the issues when one generated makefiles with
some of the custom command line options passed to CMake
and then modified the CMake file. This used to forget
about settings passed via command line.

Now it's no longer required to re-run CMake with all
custom options every time CMakeLists.txt files are
modified.
Add an option to disable OpenCL

It's not always wanted to compile OpenSubdiv with OpenCL
support when the SDK is installed on the builder machine.
Document NO_MAYA command line option

If was used in CMake but was never documented.
Make PTex support optional

Basically makes configuration log much cleaner on systems
where PTex is not installed.
Don't show warnings when OpenCL component is disabled
Fix compilation error on windows+msvc2013

- Some missing includes of <algorithms> in order to have
  stdd::min() and similar functions.
- Need to cast numIndices and numNVerts to int explicitly
  in order to solve warning treated as an error about
  precision loss.
- Can't do vector[0] for an empty vector, it'll generate
  a runtime range check error.
- MSVC only works fine with make_pair(foo, bar) syntax,
  without explicit template substitution here. Otherwise
  weird 'can't cast int to int&&' errors are happening.
Fixed build warnings/errors with VS2010 Pro
Adding a FindCLEW.cmake module in anticipation of using CLEW as a dependency