control: Drop the alternate depends on lib{egl,glx}-vendor, the default provided by mesa should always be installed.

GLX: Work around 'X_GLXCreateContextAtrribsARB' typo fix API break

Handle dlsym succeeding with info.dli_sname == NULL.

When dlsym is handed an address in a shared object that doesn't match a symbol
in that shared object (such as a C++ vtable) it returns success but sets
dli_sname to null.

Handle this case rather than crashing.

Always return an error from eglMakeCurrent if the EGLDispaly is invalid

In eglMakeCurrent, check to make sure the EGLDisplay is valid, even if the
context is NULL.

Fixes https://github.com/NVIDIA/libglvnd/issues/151

Older versions of glxproto.h contained a typo where "Attribs" was misspelled.
The typo was fixed in the xorgproto version of glxproto.h, breaking the API.

Fixes #149.

Bump the version numbers in the library filenames

If libglvnd is installed onto a system that already has non-libglvnd versions
of any of the OpenGL libraries installed, then ldconfig can get confused about
which files to create symlinks to. At worst, you could end up with a mix of the
libglvnd libraries and leftover non-libglvnd libraries.

To avoid that, bump the version numbers in these filenames:
- libGL.so.1.0.0 -> libGL.so.1.7.0
- libGLESv1_CM.so.1.0.0 -> libGLESv1_CM.so.1.2.0
- libGLESv2.so.2.0.0 -> libGLESv2.so.2.1.0
- libEGL.so.1.0.0 -> libEGL.so.1.1.0

Fixes https://github.com/NVIDIA/libglvnd/issues/147

Fix executable memory allocation ifdefs and size

In u_execmem.c, use entry_stub_size and MAPI_TABLE_NUM_DYNAMIC to determine how
much executable memory to allocate, instead of just hard-coding 256KB.

The stubs on some architectures are larger than 64 bytes, so 256KB isn't always
going to be large enough, and it's wasteful on architectures with stubs that
are smaller than 64 bytes.

Remove the #ifdefs and the Win32 and malloc-based code from u_execmem.c. It's
not needed or used anymore, and even if it was, the allocation code is in
src/utils/utils_misc.c now.

Add support for GLX_EXT_no_config_context

In testglxmakecurrent, remove the paths to test using glXCreateNewContext and
glXCreateContextAttribsARB.

The testglxcreatecontext test now tests the various context creation functions,
so we don't need to shoehorn them into testglxmakecurrent.

Add a new test, testglxcreatecontext to test the various functions for creating
GLX contexts.

It tests the core GLX functions, the GLX_ARB_create_context and
GLX_EXT_no_config_context extensions, and using a vendor-provided extension
function.

The new test is much simpler than trying to use testglxmakecurrent to test both
context creation and MakeCurrent, especially for trying to test multiple
context creation functions.

Added a glXCreateContextVendorDUMMY extension function to GLX_dummy to test
using a vendor-provided extension function to create a context. We can't use
glXCreateContextAttribsARB for that now, because it has a dispatch stub in
libGLX itself.

glXCreateContextVendorDUMMY takes the same arguments as
glXCreateContextAttribsARB, so it can also serve as an example for implementing
a dispatch stub for glXCreateContextAttribsARB in a real vendor library.

Defined a dummy attribute that a test program can use with glXQueryContext to
test dispatching by GLXContext.

The implementation of glXCreateContextAttribARB in GLX_dummy will now handle
a screen number attribute or a GLXFBConfig.

glXCreateContextAttribsARB now has a dispatch stub in libGLX.so, so the dummy
vendor doesn't need to provide one.