Sync/wait capable handler map

Added wait-capable handler map for job handlers since sometimes handler is not added to the map before some responses from gearman start to arrive.

Fix receiver race condition

Fix a race condition which occurred during job submit, echo and status calls where sometimes the waiter was not able to retrieve response from its designated channel before it was closed and recycled by the socket reader thread.

Mitigated job handle and send/receive race conditions

This release fixes the 2 following race conditions:

• race condition as described in #9
• race condition among multiple requesters submitting jobs to gearman and receiving mixed up job handles in high load situations.

add reconnect to gearman servers

• Add indefinite reconnect to gearman servers
• Add ability to client and worker to continue operating with some gearman servers offline.