Update the way we handle directories supplied by the user:
- the tarball directory is considered as a local copy, and tarballs are copied to a working area,
- the sources and build directories (CT_SRC_DIR and CT_BUILD_DIR) are now computed, and no longer an option,
- the build dir has been renamed from 'build' to 'targets'.
That should ease preparing a tarball of the resulting target.

 This is NOT the official version of dialog.  This version has been

 significantly modified from the original.  It is for use by the Linux

 kernel configuration script.  Please do not bother Savio Lam with 

 questions about this program.