Upgrade apgdiff to version 2.3.
Use `version` string in the heredoc and libexec.install lines
so we don't have to change that at the next upgrade.
Install the metafiles in `prefix`.
Use the official site as the url. Change sf.net to the mirror.
Tested on Lion using clang and llvm-gcc.
Signed-off-by: Adam Vandenberg <flangy@gmail.com>
