Specjour doesn't reassign specs if the worker is unable to run them

[elizamarcum]

For example, when we bumped rails versions from 2.3.4 to 2.3.5, my machine didn't have 2.3.5 installed and thus it wasn't able to actually run any of the specs assigned to it.

If specjour was able to notice this, it could have reassigned the specs to another worker and then there wouldn't have been any false failures.

(We're running 0.1.18)

[sandro]

This is a non-trivial fix. Hope to get it done someday.