Added definition for "user name" in definitions section.

Amended discussion of username in enrollment server section to
explain relationship (or lack thereof) between RHS of overlay name
and RHS of user name.
Fixed a spelling issue. This commit should close Issue #14 in Fluffy's tracker.
Merge remote-tracking branch 'dean/overlayname' into cj-overlayname-1
fix up checking config data
update the ConfigUpdate processing text
fix typo dean found
EKR change on when to get new config
Merge pull request #39 from fluffy/cj-overlayname-1

Cullen version of overlayname change 
update date
Clean RFC 2119 language

- Replaced RFC 2119 languages in non-normative sections.