Resolve Rspec deprecation warnings.
Update required Rescue version from 1.10 to 1.25.
Suppress deprecation warnings in specs.

Workers run in a non-forking environment in tests so set `term_child` to avoid a flood of ‘WARNING: This way of doing signal handling is now deprecated.’ output when starting each worker.
Fix use of `raise_exception`.

In Rspec 2.99 this was failing to evaluate the block and reporting:

>`raise_error` was called with non-proc object
Fix for Resque 1.25 breaking Resque::Helpers

Resque introduced a breaking change in 1.25 (https://github.com/resque/resque/commit/99a03b50d4211851dbce88caafa8f42549345858) and no longer includes `Resque::Helper` in `Resque`. See https://github.com/resque/resque/issues/1150 and https://github.com/resque/resque/issues/1168.