Check for pcntl_signal support before invoking

The pcntl_signal call is only currently supported on *nix environments,
and not even Mac at that. Check to see if the function exists before
invoking it.
Merge pull request #2 from iniq/check_pcntl_support

Check for pcntl_signal support before invoking
Allow jobs to perform a pre-run check and be requeued

There are intstances (for example when an account is in maintenance mode) that
it would be unwise to actually perform a queued task. Only the task knows what
those conditions are for itself, so we delegate the job of knowing that to the
task in the canRun() method.

But now we have three outcomes for a job: Done, Failed, and Couldn't run. Add a
new method to the QueuedTask Model to support requeuing a job that isn't
failed.
Merge pull request #3 from TribeHR/add_requeueing_and_canRun

Allow jobs to perform a pre-run check and be requeued
Add createSingletonJob

A method to conditionally queue a job, if an identical job is not already
awaiting execution.
Update docblocks to include
Merge pull request #4 from iniq/singleton_jobs

Add createSingletonJob
Moved the major folders to cakephp 2.0 structure
Moved shells to proper location for CakePHP 2.0 pluign and renamed the
Model files to comply wiht CakePHP 2.0
Fixed deprecated Displatch property
More restructuring for CkaePHP 2.0
Changed the refrences to files which names have been changed to comply
with Cakphp2.0 and PSR
Load the Plugin correctly and changed references to queue_ to queue
because file names are now Camel case
Merge pull request #5 from rgmccaw/restructure_directory_structure_for_cakephp_20

Restructure directory structure for cakephp 20
Merge pull request #6 from rgmccaw/fix_queue_for_cake_20

Fix queue for cake 20