Adds testgles2

Source code copied from: https://github.com/fantasydr/sdl-2.0-gles (thanks!)

Minor fixes, configure script changes done by me.

test/configure

@@ -587,6 +587,7 @@ LIBOBJS
 SDL_TTF_LIB
 XLIB
 GLESLIB
+GLES2LIB
 GLLIB
 CPP
 XMKMF
@@ -3860,12 +3861,49 @@ rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $have_opengles" >&5
 $as_echo "$have_opengles" >&6; }
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for OpenGL ES2 support" >&5
+$as_echo_n "checking for OpenGL ES2 support... " >&6; }
+have_opengles2=no
+cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+
+ #if defined (__IPHONEOS__)
+    #include <OpenGLES/ES2/gl.h>
+    #include <OpenGLES/ES2/glext.h>
+ #else
+    #include <GLES2/gl2.h>
+    #include <GLES2/gl2ext.h>
+ #endif
+
+int
+main ()
+{
+
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_c_try_compile "$LINENO"; then :
+
+have_opengles2=yes
+
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $have_opengles2" >&5
+$as_echo "$have_opengles2" >&6; }
+
 GLLIB=""
 GLESLIB=""
+GLES2LIB=""
 if test x$have_opengles = xyes; then
     CFLAGS="$CFLAGS -DHAVE_OPENGLES"
     GLESLIB="$XPATH -lGLESv1_CM"
 fi
+if test x$have_opengles2 = xyes; then
+    CFLAGS="$CFLAGS -DHAVE_OPENGLES2"
+    GLES2LIB="$XPATH -lGLESv2"
+fi
 if test x$have_opengl = xyes; then
     CFLAGS="$CFLAGS -DHAVE_OPENGL"
     GLLIB="$XPATH $SYS_GL_LIBS"