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.

\.exe$
\.o$
\.d$
\.a$
~$
\.orig$
/lwbasic$
/lwlink$
/lwobjdump$
/lwar$
/lwasm$
/lwcc/lwcc$
/lwcc/lwcpp$