gluegen: use parseInt, parseLong to avoid boxing unboxing an Integer/Long

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>
gluegen: avoid appending Strings in a loop, pull out a Stringbuilder we can reuse

Reuse a single stringbuilder to build all the comment strings and emit them if required.

Signed-off-by: Harvey Harrison <harvey.harrison@gmail.com>