Add routines for integer byte order conversions, floating point format

Add routines for integer byte order conversions, floating point format
and byte order conversions, and ASCII<->EBCDIC conversion.  Also add
an extensive floating point format conversion test.

The ASCII<->EBCDIC conversion used by SPSS does not correspond exactly
to any found in GNU libiconv, hence the need for a separate library.

These routines are a small part of a larger change set that I'm
breaking up for gradual submission.  Thus, they aren't used by much
yet.