piglit-dispatch: Code generation scripts.

This patch contains the code generation scripts that convert the files
gl.spec, gl.tm, and enumext.spec into C code, as well as the CMake
directives to run the scripts.

Code generation occurs in two phases: first the script
glapi/parse_glspec.py converts the .spec and .tm files into an
intermediate JSON format, which is stored in glapi/glapi.json.  Then,
the script tests/util/gen_dispatch.py converts the JSON file into two
files, tests/util/generated_dispatch.c and
tests/util/generated_dispatch.h.

There are two motivations for breaking code generation into two phases:
(1) there are other code generation tasks we may add in the future
(e.g. generating the tests/util/piglit-util-enum.c file), and it would
be nice not to have to rewrite any parsing code when we do so.  (2) if
the GL consortium ever decides to change the format of gl.spec, gl.tm,
and enumext.spec, then we only have to change parse_glspec.py.

These code generation scripts can be run by invoking "make
piglit_dispatch_gen" from the toplevel source directory.

v2: Add clarifying comments, remove a bogus "print" statement, and
raise an exception if an unrecognized multiplicity is encountered.
Also, handle "reference" multiplicity.

v3: Add APIENTRY to stub functions.  Rename "near" and "far" to avoid
problems on MSVC.  Get rid of "__" in function names.
piglit-dispatch: Add generated files.

This patch adds the files glapi/glapi.json,
tests/util/generated_dispatch.c, and tests/util/generated_dispatch.h,
which were generated using the command "make piglit_dispatch_gen".
piglit-dispatch: Remaining infrastructure.

Previous patches introduced code generation for the auto-generated
portions of the piglit-dispatch mechanism.  This patch supplies the
remaining hand-written code, which includes:

- Code to initialize piglit-dispatch.

- The actions to be taken when looking up a function, when function
  lookup fails, or when a function is unsupported.

- Code to determine whether piglit-dispatch has been initialized,
  which GL version is supported, and whether a given extension is
  supported.

- Code to look up a function using a name supplied at run-time.

- Definitions of basic GL types.

v2: Make "inline" work in MSVC.  Fix type of intermediate function
pointers.  Only try to include "glxew.h" on Linux.  Fix MSVC
definition of int8_t.  Add #include "piglit-dispatch.h" to
piglit-dispatch.c for clarity.  Get rid of "__" in function names.
piglit-dispatch: Switch to using piglit-dispatch instead of GLEW.

Previous patches set up the piglit-dispatch infrastructure but did not
use it.  This patch enables piglit-dispatch and uses it instead of
GLEW.

No piglit regressions on Intel SandyBridge (Linux) or Mac OSX.
Windows experiments
piglit-dispatch: Remove GLEW.

This patch removes the files glew.c and glew.h, which are no longer
used.  The "piglit-dispatch" mechanism is used instead.
Remove GLEW workarounds.

This patch removes workarounds that were in place to compensate for
bugs in GLEW.
Windows experiment: only do the bool workaround if not c++
glean: use piglit_get_proc_address().

Previously glean got the address of GL functions by directly calling
an OS-specific function (e.g. glXGetProcAddressARB(), dlsym(), or
wglGetProcAddress()).  This patch changes it to use
piglit_get_proc_address(), which uses piglit-dispatch.  This will help
pave the way for adapting glean to test using GLES and
forward-compatible contexts.

v2: Changed the return type of glean's getProcAddress to "void
(APIENTRY *)()" so that no type casting is necessary on Windows.
Windows experiments
Windows debug
Windows debug
Windows debug
Windows debug info
Windows experiment: always go through wglGetProcAddress
Windows experiment: cast return value from wglGetProcAddress
Windows experiment just 1.0 and 1.1 are directly bound
Windows experiment: cast return value of GetProcAddress()
Windows glean fix: make tex[] larger
Only call initialize_dispatch_pointers() if necessary