check-configuration.sh on OS X

Fixed the configuration test to look in /opt/local (instead of /opt) for MacPorts/Homebrew installations. Moved "/usr/local" to the front of the list, and the search now breaks on the first binary found. (Later I'll add code to allow continuation if the version turns out to be too low.) Presumably the precedence of binaries can be counted on to be /usr/local > /opt/local > /usr/pkg > /usr. The script can now find installed versions of make and gcc on OS X. I've also added a test for Sparkle, only on Darwin, to check_misc.