1122530: Improved grammar and abbreviation usage.

Made some changes to the man pages and some displayed strings to improve
the grammar and reduce the usage of select abbreviations and terms.

Additionally, the man pages for the rhn-migrate-classic-to-rhsm and
sat5to6.8 have been updated to reflect changes to the options and
functionality (bug 1145828).
Merge pull request #1035 from candlepin/crog/1122530

1122530: Improved grammar and abbreviation usage.