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/GLExtensions.cpp

@@ -129,7 +129,7 @@ bool osg::isGLExtensionOrVersionSupported(unsigned int contextID, const char *ex
                     #  ifndef GL_NUM_EXTENSIONS
                     #    define GL_NUM_EXTENSIONS 0x821D
                     #  endif
-                    GLint numExt;
+                    GLint numExt = 0;
                     glGetIntegerv( GL_NUM_EXTENSIONS, &numExt );
                     int idx;
                     for( idx=0; idx<numExt; idx++ )