allocate port automatically for mirror and rest servers

[giraudsimon]

... to allow multiple SpecTcl instances at same time.

[rfoxkendo]

I assume this means putting the changes I suggested to Dirk in the SpecTclInit.tcl file that's given in the documentation.
A couple of things to think about:

• Should this SpecTclInit.tcl be in Skel? If so then new users of SpecTcl get it automatically but on the other hand if users are not using CutiePie, ReST and Mirror servers are unnecessary overhead.
• If we start running the port manager server from NSCLDAQ in the interactive analysis systems (whatever fishtank becomes), We can make that the default way to get an unused port and that's simpler than the whole search for an unused port (which BTW I think I do in tclhttpd/ReST's start-up (search for an unused port starting with the HTTPDPort given.

If the latter is done it might be useful to pull the Tcl port manager client package into SpecTcl so that we don't have a dependency on daqstartup.bash being sourced.

"We do this not because it is easy
We do this because we thought it would be east"