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/VertexProgram.cpp

@@ -150,7 +150,7 @@ void VertexProgram::apply(State& state) const
                                      _vertexProgram.length(), _vertexProgram.c_str());
 
         // Check for errors
-        GLint errorposition;
+        GLint errorposition = 0;
         glGetIntegerv(GL_PROGRAM_ERROR_POSITION_ARB, &errorposition);
         if (errorposition != -1)
         {