r.bilinear float-ized

[Angus Carr]

If anyone is interested, I have adapted r.bilinear to work with float
rasters. I am currently doing some bug-testing, and I will be adapting it
to work with doubles, floats and integer rasters. So far, it compiles
under Linux, using the standard head file provided. I'm sure I haven't
changed anything significant that would make it no longer compile
elsewhere.

Angus Carr.