Fix WordPress update issues on local Apache sites by updating Apache's User and Group
Credit goes to Justin Kopepasah: Change Local Apache User on a Mac (Mavericks)
Apache permissions on Mac (Mavericks) prevents uploads on certain local environments, particularly updating of WordPress' core and plugins (WordPress will ask for FTP credentials).
To fix this, change Apache's default User and Group.
# /etc/apache2/httpd.conf
User [your_username]
Group staff
Then restart apache:
$ sudo apachectl restart