At least with my AMD card, in case of SAL_FORCEGL=1 the startup crashes
quite early. DrMemory says:

~~Dr.M~~ Error #1: UNADDRESSABLE ACCESS: writing 0x00001414-0x00001415 1 byte(s)
~~Dr.M~~ # 0 atioglxx.dll!DrvPresentBuffers                          +0xd6ea6  (0x09a248f6 <atioglxx.dll+0x1248f6>)
~~Dr.M~~ # 1 atioglxx.dll!DrvPresentBuffers                          +0x3c069c (0x09d0e0ed <atioglxx.dll+0x40e0ed>)
~~Dr.M~~ # 2 vcllo.dll!OpenGLContext::InitGLEW                        [c:\lo\master\vcl\source\opengl\openglcontext.cxx:949]
~~Dr.M~~ # 3 vcllo.dll!OpenGLContext::ImplInit                        [c:\lo\master\vcl\source\opengl\openglcontext.cxx:866]
~~Dr.M~~ # 4 vcllo.dll!OpenGLContext::init                            [c:\lo\master\vcl\source\opengl\openglcontext.cxx:786]
~~Dr.M~~ # 5 vcllo.dll!WinOpenGLSalGraphicsImpl::CreateWinContext     [c:\lo\master\vcl\opengl\win\gdiimpl.cxx:36]

Turns out that in order to enable the GL_DEBUG_OUTPUT_SYNCHRONOUS_ARB
extension, the GL context must be created with WGL_CONTEXT_DEBUG_BIT_ARB
set. It seems that other drivers did not enforce this so far, but in
this case the driver just crashes without this.

Fix the problem by splitting out the debug setup part of InitGLEW() into
a new InitGLEWDebugging(), and at least on Windows call it only after
wglCreateContextAttribsARB() and wglMakeCurrent(). Additionally make
sure that in the debug case the necessary flag is passed to
wglCreateContextAttribsARB().

Conflicts:
	vcl/source/opengl/OpenGLContext.cxx

Change-Id: I6b77e0c06fd85fdae0386a0801f1de1838524586
Reviewed-on: https://gerrit.libreoffice.org/17750Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>
Reviewed-on: https://gerrit.libreoffice.org/18219Reviewed-by: Jan Holesovsky <kendy@collabora.com>
Tested-by: Jan Holesovsky <kendy@collabora.com>