Fix 'repl :connect <port>' when used outside of a project [fixes #1344]

connect-string now verifies that the string ends with a port after the
string is fully formed, aborting if no port is found. This also
includes improvements to the repl help text, and more test coverage
for connect-string.
Merge pull request #1345 from tobias/repl-port-abort-fix

Fix 'repl :connect <port>' when used outside of a project [fixes #1344]