mesa: Use a recursive mutex for the texture lock.

This avoids problems with things like meta operations calling functions
that want to take the lock while the lock is already held.  Basically,
the point is to guard against API reentrancy across threads...not to
guard against ourselves.

Dave Airlie opposed this change, but it makes master usable again and no
one proposed a better solution.  We can revert this if/when someone
does.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>
Tested-by: Chris Forbes <chrisf@ijw.co.nz>

src/mesa/main/shared.c

@@ -113,7 +113,7 @@ _mesa_alloc_shared_state(struct gl_context *ctx)
    assert(shared->DefaultTex[TEXTURE_1D_INDEX]->RefCount == 1);
 
    /* Mutex and timestamp for texobj state validation */
-   mtx_init(&shared->TexMutex, mtx_plain);
+   mtx_init(&shared->TexMutex, mtx_recursive);
    shared->TextureStateStamp = 0;
 
    shared->FrameBuffers = _mesa_NewHashTable();