Do not set SO_REUSEPORT.

This allows multiple processes to bind to the same addr/port which is
not desirable.

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2703 ba6dc0ae-232f-0410-883f-9ebac64fc565
Fixes for dmtcp_launch --no-coordinator.

- The process now listens on the given port.
- dmtcp_command can be used to communicate with the process.

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2704 ba6dc0ae-232f-0410-883f-9ebac64fc565
Added --port-file flag to dmtcp_{launch,restart}.

git-svn-id: svn://svn.code.sf.net/p/dmtcp/code/trunk@2705 ba6dc0ae-232f-0410-883f-9ebac64fc565