Fix bug with section padding and downward allocation. When placing sections with the "high" method, padding was added to the section instance at the lowest address insted of the highest as is appropriate for the padafter option. Explicitly handle the padding for the first instance encountered (highest address) when growing down.

See the file GPL3 for a copy of the GNU General Public License, version 3,
under which the majority of this distribution is licensed.

Some specific source files, including many of those in the lwcc subdirectory
are licensed differently. See each individual file for specific details.