build.sh release failure with relative path

["Christoph Egger" <Christoph_Egger%gmx.de@localhost>]

Hi!

When $KERNOBJDIR is a relative path then build.sh release fails
with 

      nbconfig: cannot create $KERNOBJDIR/GENERIC

There are two ways to fix this:

1. Fix nbconfig to prepend prefix to builddir specified via -b
2. Fix call to nbconfig by prepending prefix to the kernel config
   file (removes change directory to kernel config dir)

What is the way to go?

Christoph