st/wgl: fix implementation of wglCreateContextAttribsARB()

st/wgl: fix implementation of wglCreateContextAttribsARB()

wglCreateContextAttribsARB() didn't work previously since it returned
a context ID that wasn't allocated by OPENGL32.DLL.  So if that context
ID was later passed to wglMakeCurrent(), etc. it was rejected.

Now when wglCreateContextAttribsARB() is called we actually call
wglCreateContext() in order to get a valid context ID.  Then we
replace the context data which was created with new context data
which reflects the arguments passed to wglCreateContextAttribsARB().

If there were a DrvCreateContextAttribs() function in the ICD this
work-around wouldn't be necessary.

Reviewed-by: Charmaine Lee <charmainel@vmware.com>
Conflicts:
	src/gallium/state_trackers/wgl/stw_ext_extensionsstring.c
	src/gallium/state_trackers/wgl/stw_getprocaddress.c