Improve update checking

[star-szr]

Two things:

1. As a workflow tool I don't want virtualhost.sh to interrupt or disrupt the user too much. The next release will decrease the automatic update checking to once a day to help this a bit. For non-Homebrew users I would like the update checking to be even less disruptive, especially because the update checking seems to take at least a second or three.
2. Homebrew users should at least get some different instructions for updating. Can we detect Homebrew users? Can we/should we disable auto update checking for Homebrew users?