os: change UserConfigDir on Darwin to ~/Library/Application Support
The old code used ~/Library/Preferences, which is documented by
Apple as:
This directory contains app-specific preference files. You
should not create files in this directory yourself. Instead, use
the NSUserDefaults class or CFPreferences API to get and set
preference values for your app.
It looks like we missed everything after the first sentence; it's
definitely not the right choice for files that Go programs and users
should be touching directly.
Instead, use ~/Library/Application Support, which is documented as:
Use this directory to store all app data files except those
associated with the user’s documents. For example, you might use
this directory to store app-created data files, configuration
files, templates, or other fixed or modifiable resources that
are managed by the app. An app might use this directory to store
a modifiable copy of resources contained initially in the app’s
bundle. A game might use this directory to store new levels
purchased by the user and downloaded from a server.
This seems in line with what UserConfigDir is for, so use it.
The documentation quotes above are obtained from the surprisingly long
link below: