Bug 801: Fix VBAA Distortions (VBO-size fractional delta) and AA (Sample fragment position and count)

Inflating the FBO pixel-size of the region using a 'samples count'
multiplier to the projected window bounding box
allows controlling the AA distortion as well as defining the
fragment position due to it's grid-fitting nature, see below.

- Fix VBAA Distortions (FBO-size fractional delta)
  Inflated framebuffer exceeds 'box-size * sampleCount'
  since it must be the ceiling of the latter due to it's integer number nature.
  This difference either must reflect the texture-coords -or- the
  texture bounding vertices-box in the 2nd pass, otherwise a distorion will appear
  which is quite visible explicit w/ text.
  Using texture-coords is not suitable, due to floating point accuracy,
  hence this patch extends the texture bounding vertices-box about the ceiling delta.

  A comparible distortion existed with the previous implementation as well,
  since it used an arbitrary FBO-size and hence the magnification was not grid-fitting.

  Current implementation is grid-fitting, or at least matches the non-inflated grid,
  since it inflates the original window-size of the region about samples-count.

- AA (Sample fragment position and count)
  Using a sample-count w/ a multiple of 2 (currently 2, 4 and 8 are properly implemented),
  based on the projected window bounding box will give the 2nd-pass fragment shader (AA)
  a fragment-postion in center of the sample pixels exposing one AA pixel.
  Hence we need to use the diagonal coords (NW, SW, ..) off by half a pixel
  to reach the 1st sample-pixel .. and 1.5 pixels to reach the 2nd .. and so forth.