ISSUE-2345: 15.17 feGaussianBlur [SVG 1.1 F2 Last Call]

ISSUE-2345: 15.17 feGaussianBlur [SVG 1.1 F2  Last Call]

http://www.w3.org/Graphics/SVG/WG/track/issues/2345

Raised by: Erik Dahlström
On product: SVG 1.1 F2  Last Call

it is nice to see, that the formula for the y dimension is
added for the feGaussianBlur.
Nice as well to get now the input image for standard deviation zero.

Minor cosmetic questions/suggestions:
a) Why is H(x) styled in black, I(y) in red?
b) Why is the approximation formula only for s available?
(should be sufficient to write, that the approximation applies
for the t correspondingly)
c) Maybe worth to mention, that for something like stdDeviation="1 0" 
or stdDeviation="0 1" with '1' representing something different from
0, the mathematically expected result is not the input image. 
It is only a blur in one direction.
However, because the definition does not explictly mention
this case, implementations will hopefully do it as mathematically
expected.

Original mail:
http://lists.w3.org/Archives/Public/www-svg/2010Jun/0201.html