[R] 2-dimensional convolution tool wanted

[Carl Witthoft]

I found the imgConvolve tool in the biOps package, but since I'm 
primarily working on OSX computers, wondered if there are any other 
2-dimensional convolution functions out there?
And, yes, I'm going to ask r-sig-mac whether biOps will compile from 
source under OSX.

I did find one convolution function somewhere, but it was limited to 
three built-in kernels, so not really helpful.

thanks
Carl