Fix the zero padding so that it doesn't crash if tehre is more than 1K of

Fix the zero padding so that it doesn't crash if tehre is more than 1K of
padding required.

Fix the shared library support which,  although the library is at a high
address,  we don't want to pad the file to +16Mb.  We also do not want the
relocations starting +16Mb into the file :-)