user/jszakmeister: don't hardcode my home directory
user/jszakmeister: look in /usr/local for ctags

The intent of all of this is to make launching the MacVim GUI by
double-clicking a supported file work correctly when using a custom
ctags.  If a user has not set up their launchd configuration to match
the PATH configuration set by the shell, then Vim will be unable to find
a good ctags binary on Mac OS X.