Import JOB_UNKNOWN at top-level.
Add SSL support.

This adds support for SSL connections to an SSL enabled job server.
To use SSL, three SSL-related files must be given when defining a
job server connection:

  keyfile - File with the private key
  certfile - File with the public key
  ca_certs - File with the CA public cert(s)

GearmanConnectionManager has been modified to simultaneously
support non-SSL and SSL connections alike. Nothing changes for
non-SSL connections:

  GearmanClient(['localhost:4730'])

SSL connections require that the host list use a dictionary to
define the connection:

  s1 = { 'host': 'localhost',
         'port': 4730,
         'keyfile': '/path/to/keyfile',
         'certfile': '/path/to/certfile',
         'ca_certs': '/path/to/ca_certs' }
  GearmanClient([s1])

Currently, all three SSL related files MUST be given and the port
must be specified in the dictionary.
Merge pull request #41 from Shrews/master

Import JOB_UNKNOWN constant.
Merge pull request #43 from Shrews/ssl_support

Add SSL support.
Require cert validation of server.
Merge pull request #45 from Shrews/ssl_fix

Require cert validation of server.
Add support for SUBMIT_JOB_EPOCH

* submit_job now accepts a 'when_to_run' parameter to take advantage of
  Gearman's ability to schedule jobs to be run in the future