do HTML escaping on error pages

Lukas Reschke (via Stephan Rickauer) points that arguments that don't
pass the assertion checks make it to the exception page unescaped.

Move niftyString() to interface-lib.php to make it available in
exceptions.php and modify InvalidArgException::__construct() and
dumpArray() to use it.
refine some wording in genericAssertion()
refine VLAN compound key assertion checks

Replace "uint-uint" assertion with "uint-vlan" and "uint-vlan1" and make
use of these in respective ophandlers such that these attribute a
malformed VLAN compound key to user's input (InvalidRequestArgException)
rather than an internal error (InvalidArgException).
fixup a few non-breaking space entities
the 2nd TITLE in getOpLink() was a bug