R1:60d2b743d900

Print out stack traces when Aphlict server dies

Summary: Printing out `err` is less informative than `err.stack`, which has the message, type, //and// a trace.

Test Plan:
Faked an exception, then:

```
$ sudo ./bin/aphlict debug
Starting Aphlict server in foreground...
Launching server:

$ 'node' '/INSECURE/devtools/phabricator/src/applications/aphlict/management/../../../../support/aphlict/server/aphlict_server.js' --port='22280' --admin='22281' --host='localhost'

[Wed Jun 11 2014 10:20:39 GMT-0700…