Bug 879511 - [email/IMAP] date-time parsing regex does not accept legal "SP DIGIT" syntax

also removes speculative parseImapDate logic function that is not used.
Merge pull request #217 from asutherland/imap-date-time

Bug 879511 - [email/IMAP] date-time parsing regex does not accept legal "SP DIGIT" syntax. r=lightsofapollo