JSocket: Retry connect() on ECONNREFUSED.

- Currently we retry ten times with 100ms sleep in between.

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2462 ba6dc0ae-232f-0410-883f-9ebac64fc565
Show errno on failure to connect to coord.

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2463 ba6dc0ae-232f-0410-883f-9ebac64fc565
Increase coord listenSock backlog to 128.

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2464 ba6dc0ae-232f-0410-883f-9ebac64fc565