add support for GL_EXT_debug_marker

This extension is always added to the GL_EXTENSIONS
extension string for the current GL context, regardless
of if it's supported by the h/w driver.

The extension itself will be handled by GLES_trace (eventually),
when GLES_trace is not enabled, it'll result to a no-op.

If the h/w implementation has this extension, we'll call that version
instead of our dummy version.

Change-Id: Ie5dd3387c4d45cd5ed5f03b73bda6045620a96bc
diff --git a/opengl/libs/GLES2/gl2_api.in b/opengl/libs/GLES2/gl2_api.in
index 5164450..9a89a52 100644
--- a/opengl/libs/GLES2/gl2_api.in
+++ b/opengl/libs/GLES2/gl2_api.in
@@ -211,7 +211,7 @@
 void API_ENTRY(glGetShaderSource)(GLuint shader, GLsizei bufsize, GLsizei* length, GLchar* source) {
     CALL_GL_API(glGetShaderSource, shader, bufsize, length, source);
 }
-const GLubyte* API_ENTRY(glGetString)(GLenum name) {
+const GLubyte* API_ENTRY(__glGetString)(GLenum name) {
     CALL_GL_API_RETURN(glGetString, name);
 }
 void API_ENTRY(glGetTexParameterfv)(GLenum target, GLenum pname, GLfloat* params) {