pipe: Use empty message token '--' if no message

Previously, the subject was duplicated, which is really confusing
pipe: Unwrap forwarded emails

If the mail received into the system has a content type of 'message/rfc822',
then unwrap the inner message and use it as the parsed email. Effectively,
assume the email was forwarded as an message/rfc822 attachment.
pipe: Honor inline bodies as valid message

Previously, if a message had a Content-Disposition header, then it could not
be considered as the body of the message.
fetch: Implement parsing attached email

If the content of the message is of type `message/rfc822`, then support
downloading the body of the message and sending it off to the mail parsing
system, simulating a piped email.
Merge pull request #482 from greezybacon/issue/email-parse-issues

Fixup a few email piping issues

Reviewed-By: Peter Rotich <peter@osticket.com>
Use case-insensitive matching on email address

This patch addresses an issue where a client may have upper-case letters in
their email address. When visiting the client portal to check the ticket
status, previously, the exact same case would be required in the 'Email
Address' box.

This patch removes the case sensitivity for email logins.
Merge branch 'develop' into develop-next

Conflicts:
	include/class.usersession.php