From David Fries, "Fix remote X11 crash querying GL_NUM_EXTENSIONS

In osg::isGLExtensionOrVersionSupported in src/osg/GLExtensions.cpp when
using indirect X11 rendering,
glGetIntegerv( GL_NUM_EXTENSIONS, &numExt );
is leaving numExt uninitilized causing the following glGetStringi to
return NULL when the extension number isn't present.  Passing NULL to
std::string() then crashes.  This is with the following nVidia driver.
OpenGL version string: 3.3.0 NVIDIA 256.35

I went ahead and initialized some of the other variables before
glGetInitegerv in other files as well.  I don't know for sure
which ones can fail, so I don't know which are strictly required.
"

src/osg/State.cpp

@@ -899,7 +899,7 @@ void State::initializeExtensionProcs()
                                  osg::isGLExtensionSupported(_contextID,"GL_EXT_multitexture") ||
                                  OSG_GLES1_FEATURES)
     {
-        GLint maxTextureUnits;
+        GLint maxTextureUnits = 0;
         glGetIntegerv(GL_MAX_TEXTURE_UNITS,&maxTextureUnits);
         _glMaxTextureUnits = maxTextureUnits;
         _glMaxTextureCoords = maxTextureUnits;