Replace vars in include lines in .repo files. BZ 977380
Add upgrade-minimal typos from man page.
Fix update-minimal typo from man page.
Add repo argument to RepoError, so we can easily set it to tell which one.
Add repo= arguments to almost all RepoError raises, so we don't print unknown.
Check /usr for writability before running a transaction.
Check for existance, so mock etc. is happy.