hdf5_der

[svn-r17234] Improvement:
Added code to catch the exit code of the Generator.

Bug fixes:
Was doing "exit $nerrors" which is bad since Unix exit size
is defined as a small unsigned value.  Changed it to exit 0
if no error, exit 1 if errors found.

Cosmetic change:
Rearrange some code locations so that it is cleaner and more
logical.

Tested:
Jam and Linew.