Be paranoid of Thor

For some reason, when thor is a dependency (but not required) and guard
is required, a `Thor` class is created without actually requiring thor.
This caused and error when attempting to call `Thor.no_commands` (#78).

`Thor.no_commands` was added as of version 0.18.0, so that's the
earliest version we'll support.
Release 1.15.1
Update changelog
Always require honeybadger/monitor

Integrations depend on it now.
Rails 2 has no Railtie
Release 1.15.2
Send User-Agent
Include more info in User-Agent, freeze hash.
Freeze other constants
Passenger/forked process support.
Don't log sending data unless there is some.
Unlock mutex on fork, before clearing data.
Add missing Honeybadger::Monitor dependency to integrations.
Add spec for passenger integration
#fork if forked.
Update changelog
Test #fork
Release 1.15.3
Use gzip compression when contacting server.