* Macports build instructions were incomplete. The main blocker was that
packages/darwin_app/embed-MacOSX-dependencies.sh is hard-coded to use
homebrew paths instead of Macports or Fink paths. That could be fixed,
but there are bigger problems:
a) having two build environments splits the developer knowledge-base in
half and potentially doubles the number of build issues
b) Macports requires full XCode which is multi-gigs of download and
probably hours more of installation time. In fact I ran out of space on
my OSX VM just from the App Store trying to update XCode!

parse options before downloading nwjs binary (since some of the nwjs binary prep depends on whether we're building a dmg)

If compiling an OSX dmg, don't try to change permission on a file which doesn't exist for that platform

Add support for loading and storing the MIDI API preference (commit 516eba76 from vanilla by aib <aibok42@gmail.com>, slightly edited.

Keep track of the number of audio and MIDI device entries in the preferences, to avoid zombie entries on Mac and Windows. Proposed fix for #213, needs testing on Mac and Windows.

another attempt to fix #218: get deterministic, sequential behavior when substituting the "nwjs" string for "Purr Data" in the OSX app bundle

Fix up misleading tooltips for the Ok/Apply/Close buttons of the Preferences dialog. These apply to the prefs dialog as a whole, not just to the audio properties.

first shot at fixing issue #218: error when trying to install on OSX. See if using a temporary text file will work around the bug of plutil creating empty files