merge: upstream changes

 * Factor out rfc2047_decode_envelope()
 * Parse and store mime headers in the BODY
 * Add mx operation save_to_header_cache
 * Add protected header received email support
 * Add rfc2047_encode_envelope helper
 * Refactor save_fcc() function
 * Move fcc after send
 * Prompt when mutt_write_fcc() fails
 * Refactor postpone_message()
 * When postponing, encode descriptions before encrypting
 * More postpone cleanup
 * Fix flags if mutt_get_postponed() has no messages
 * Display mail sent message after Fcc finishes
 * Handle improperly encoded pgp/mime octetstream part
 * Add config and data structure for protected header write support
 * Add a new mode for mutt_write_rfc822_header()
 * Finish protected header write support
 * Read in protected headers when resuming a postponed message
 * Free pgpkeylist if the send fails
 * Rfc2047 encode and fold X-Label when writing updates
 * Restore the xlabel_changed reset
 * Make a copy of x_label before encoding it for updates
 * spelling consistency
 * Updated French translation
 * Added support for the "light" color prefix (in addition to "bright")
 * Light colors: do not do the + 8 on negative values, such as COLOR_DEFAULT
 * Create envelope->changed to mark all field changes
 * Change x-label editing flag to be in the envelope
 * Add $crypt_protected_headers_save
 * Color protected subject as a header in the pager
 * Respect ignore for the protected subject display
 * fix config order
 * Remove unused MUTT_FORMAT_MAKEPRINT flag
 * Sleep $sleep_time after displaying "mail sent" message
 * Update copyright for the next stable release