[Users] Parse PGP/MIME headers emitted by GPGMail + Exchange [patch]

[Michael Gmelin]

This patch allows claws to read PGP encrypted email created by GPGMail
over the Exchange plugin of Mail.app on Mac OS X:
http://www.thewildbeast.co.uk/claws-mail/bugzilla/show_bug.cgi?id=3632

It would be cool if one of the developers could take a look at it and
give some feedback.

Thanks & sorry for nagging,
Michael

-- 
Michael Gmelin