Environment
===========
Mesa on my linux box compiled with built-in gles1 and gles2. 
Both opengl and opengles were enabled in SDL (rev 6302) by default.

BUGS
====
1. SDL_CreateWindow(title, x, y, w, h, SDL_WINDOW_SHOWN | SDL_WINDOW_OPENGL) return NULL and can't get any error message from SDL_GetError().
   
2. Window can be created with window = SDL_CreateWindow(title, x,y, w, h, SDL_WINDOW_SHOWN), but SDL_CreateRender(window, -1, SDL_RENDERER_ACCELERATED) return NULL. SDL_GetError() return  "Couldn't find matching render driver". 


Workaround
==========
Compile SDL with --enable-video-opengles=no.

A rough analysis of bug1
========================
Those bugs may be due to this(not sure):

src/video/SDL_video.c
SDL_Window *
SDL_CreateWindow(const char *title, int x, int y, int w, int h, Uint32 flags)
{
...
#if (SDL_VIDEO_OPENGL && __MACOSX__) || __IPHONEOS__ || __ANDROID__
    flags |= SDL_WINDOW_OPENGL;
#endif
    if (flags & SDL_WINDOW_OPENGL) {
        if (!_this->GL_CreateContext) {
            SDL_SetError("No OpenGL support in video driver");
            return NULL;
        }
        SDL_GL_LoadLibrary(NULL);
    }
...    
    if (_this->CreateWindow && _this->CreateWindow(_this, window) < 0) {
        SDL_DestroyWindow(window);
        return NULL;
    }
...



src/video/x11/SDL_x11video.c:

static SDL_VideoDevice *
X11_CreateDevice(int devindex)
...
#if SDL_VIDEO_OPENGL_ES || SDL_VIDEO_OPENGL_ES2
    device->gles_data = (struct SDL_PrivateGLESData *) SDL_calloc(1, sizeof(SDL_PrivateGLESData));
    if (!device->gles_data) {
        SDL_OutOfMemory();
        return NULL;
    }
#endif
...
#if SDL_VIDEO_OPENGL_GLX
    device->GL_LoadLibrary = X11_GL_LoadLibrary;
    ...
#endif
#if SDL_VIDEO_OPENGL_ES || SDL_VIDEO_OPENGL_ES2
    device->GL_LoadLibrary = X11_GLES_LoadLibrary;
    ...
#endif

So X11_GLES_LoadLibrary will be called and gl_data will be NULL if both gles and glx are enabled. 

src/video/x11/SDL_x11window.c:
int
X11_CreateWindow(_THIS, SDL_Window * window)
...
#if SDL_VIDEO_OPENGL_GLX
    if (window->flags & SDL_WINDOW_OPENGL) {
        XVisualInfo *vinfo;

        vinfo = X11_GL_GetVisual(_this, display, screen);
        if (!vinfo) {
            return -1;
        }
        visual = vinfo->visual;
        depth = vinfo->depth;
        XFree(vinfo);
    } else
#endif
#if SDL_VIDEO_OPENGL_ES || SDL_VIDEO_OPENGL_ES2
    if (window->flags & SDL_WINDOW_OPENGL) {
        XVisualInfo *vinfo;

        vinfo = X11_GLES_GetVisual(_this, display, screen);
        if (!vinfo) {
            return -1;
        }
        visual = vinfo->visual;
        depth = vinfo->depth;
        XFree(vinfo);
    } else
#endif

If X11_GL_GetVisual return NULL, X11_GLES_GetVisual will not be called.

src/video/x11/SDL_x11opengl.c:
XVisualInfo *
X11_GL_GetVisual(_THIS, Display * display, int screen)
{   
... 
    if (!_this->gl_data) {
        /* The OpenGL library wasn't loaded, SDL_GetError() should have info */
        return NULL;
    }
...

Since X11_GL_LoadLibrary was not called, _this->gl_data  was NULL. So X11_GL_GetVisual return NULL. Then SDL_CreateWindow return NULL.