Merge branch 'release/v2_3_4' into dev
Fix ptexViewer: enable specular pass in both IBL and point lighting
Fix UV merging in osdPolySmooth code example

Because our plugin sets UVs with individual face-varying vertices,
Maya interprets the buffer as discontinuous everywhere. Adding a
node in the graph that merges UVs along non-boundary edges resolves
this problem (until the plugin outputs the UV vertex indices in
an aggregated manner).
Fix glViewer support for GLSL compute

Core-profile request code was incorrect: we need to request GL 4.3 core profile whenever available.

fixes #254
Fix build warnings (optimized)
Adding the ability to read obj files to the dxViewer example

(passed from command line!)
Adding screen-capture function to ptexViewer

- renders off-screen a higher resolution version of the current view
- saves the render to image files (screenshot.x.png)
- modified the background color to have alpha set to 0 (screenshots can be composited)
Move VBO buffer allocation out of allocate() and into BindVBO()

fixes #256
Fixed ptexViewer shader errors.
Modified ptexViewer and uvViewer shaders to address some portability issues.
Enable uvViewer on OS X now that Mavericks is released.
Fixes black texels when the resolution of a ptex face is less than 4.
Closes #253
Replacing un-necessary dynamic_cast with reinterpret_cast within FarDispatcher

First step in removing RTTI from Far and Hbr - further fixes require modifications of Hbr
and will tackled in another fix.

fixes #257
Fixed a build error when using older versions of GLFW
Fix Gregory Boundary patch buffer overrun

Prevent boundaryEdgeNeighbors[2] from being overrun when an interior
vertex has more than 2 boundary neighbor vertices. The fix is applied
to the GLSL / HLSL and CPU implementations.

Note: this appears to fix long-standing problems with Gregory patches,
but i am not entirely convinced that this fixes the general case.

fixes #259
Minor code cleanup of FarMeshFactory
Fix Zlib include in ptexViewer

libpng 1.5 does not include zlib.h anymore (good !) - now we have to do it ourselves.

fixes #261
Update documention for Xcode builds
Fix GLSL array instantiation syntax for glStencilViewer

fixes #263
Fixed examples to run correctly on high DPI displays with GLFW 3

The example code now uses the new glfw*FramebufferSize methods
to determine the size of the windows's framebuffer for rendering
and glfw*WindowSize method for user interaction

Fixes #263