Fix errant variable access

Another case where Smarty is now erroring about this but previously
was silent.

Change-Id: Ice53021af4e92874ffb4ac35561012fd2ac72add
Add general troubleshooting and debugging tips

Having just included three of these four in a forum post it seemed
silly that we don't already have these in the docs. If/when the
debugging video appears, it could easily be inserted here too.

2014-12-05 Patch set 3: remove words for clarity and correctness.
2014-12-06 Patch set 4: fix casing, clarify alternatives to print
                        statements in non-software.

Change-Id: I18e66b4ee58d8a6e2dbe9be854a63d918d63aef3