Explicitly provided --port flag in xsp4 walkthrough

This should (hopefully) prevent some novice headaches, given that the default xsp4 port number apparently varies from download to download right now (e.g., Mac OS X MDK .pkg 3.10 still uses port 8080 as default).
Merge pull request #61 from DasAllFolks/gh-pages

Explicitly provided --port flag in xsp4 walkthrough