Misc OSX porting things:

* autostart the assistant on OSX, using launchd **done**
* icon to start webapp **done**
* use FSEvents to detect file changes (better than kqueue) **done**
* Use OSX's "network reachability functionality" to detect when on a network
  <http://developer.apple.com/library/mac/#documentation/Networking/Conceptual/SystemConfigFrameworks/SC_Intro/SC_Intro.html#//apple_ref/doc/uid/TP40001065>

Bugs:

[[!inline pages="tagged(design/assistant/OSX) and !link(bugs/done)" show=0 archive=yes]]
