util: string, fall back to string length if Unicode.width fails
test, string length: make sure bad message line has length
util: comment on fall back
person: Don't downcase the email address

As per RFC 2821:
    The local-part of a mailbox MUST BE treated as case sensitive.
    Therefore, SMTP implementations MUST take care to preserve the case of
    mailbox local-parts. Mailbox domains are not case sensitive. In particular,
    for some hosts the user "smith" is different from the user "Smith".
Merge #256: Fix missing lines because of incorrect line width calculation
Run travis on 2.1.0, but allow failure

Issue #266 needs to be resolved before tests pass.
Merge branch 'develop' into maildir-root