Fixes the way spinsv kills the process.

Now spinsv sends SIGTERM followed by a configurable grace period
before a SIGKILL. User defined kill commnad preceeds above if
given.

Other changes include compatibitlity with GHC 7.4.2:

 - forkFinally is backported.
 - Net.PortID is replaced by NetPortId that is a Show
 - Some namepace ambiguities replaced by qualified names.

Patch by Omid Aladini <omid@soundcloud.com>
         Emily Green  <em@soundcloud.com>