modify dependency tracking code so that it:

modify dependency tracking code so that it:
1) inserts the pathname of the object file in the dependency file
   (currently, gcc will only generate the basename)
2) the directory tree within .deps mirrors the source tree, so that we use
   shorter filenames
problem 1 was reported to me by Tom Angert <angert@bellsouth.net>
(This used to be commit 274a2cff30f7325d1bc1647075a6c4f887e42e4f)