15.0/relnote: Tidy application changes and contributed software

+ remove expat, this is a private lib and doesn't have a manual
+ move the thing that is changing to the beginingish of the sentences
+ s/foo/the foo frobber/ to match usual freebsd style
+ fix some markup and punctuation typos

These need to happen before the entries can be alphabetized.

Discussed with: jhb, olce (loosely)