Add swap-byte-order.sh to test libexif's byte order conversion function.

Add swap-byte-order.sh to test libexif's byte order conversion function.

This is accomplished by adding a feature to test-parse.c to switch the
byte order before dumping the EXIF output. Additionally, the MakerNote
values are now logged in the dump as well, in the same way as the
regular tags, to better catch regressions.

This new test uncovered a bug in the decoding of the
MNOTE_NIKON_TAG_FIRMWARE tag whose data should not be treated as being
endian-specific.