Made build tmp directory configurable via TMPDIR.

The build process was originally hard coded to use /tmp but some
systems mount /tmp with noexec, causing the build to fail.  This
change allows the user (optionally) to specify a tmp dir.  E.g.,

TMPDIR=~/tmp make
Make start udp server log message more detailed.

Originally it logged the same message when either the port or database
config settings were wrong.  Now it logs which setting was wrong.
Merge pull request #665 from dgnorton/master

Change to build process and a log message.