Fix handling of uuencoded messages if messages_cache is enabled (#1490108)

Conflicts:
	program/lib/Roundcube/rcube_message.php
Fix handling of base64-encoded attachments with extra spaces (#1490111)
Fix handling of UNKNOWN-CTE response, try do decode content client-side (#1490046)
Fix "PHP Fatal error: Cannot redeclare class PEAR" if both program/lib/PEAR.php and composer loaders exist (#1490112)
Really fix UNKNOWN-CTE handling
Fix compatibility with PHP 5.2. in rcube_imap_generic (#1490115)
raoulbhatia: Custom changes