This is needed to allow updating the visible rect before invalidating
the DCEs.

The ActivateContext in SetRenderTarget was an old regression prevention,
but now it is time to remove it.

There is no need for _BLIT usage. RESOURCELOAD should be faster.

SetupForBlit sets up the GL viewport and projection matrix for
screen-cordinate access to the framebuffer. These settings were not
updated if the other gl states were already set up for blitting. Guild
Wars reads back an offscreen rendered texture from the framebuffer,
which currently sets up CTXUSAGE_BLIT, then changes the render target,
and draws to the texture, which has to be reloaded from system memory
before it can be rendered to(since GW loaded some data into it). If the
two render targets had different size this failed.

The test used D3DPOOL_MANAGED which is mutually exclusive with
RENDERTARGET usage, thus the call failed.