Update b4 to rev 4 via SR 823294
    
    https://build.opensuse.org/request/show/823294
    by user jirislaby + dimstar_suse
    - Update to version 0.5.2:
      * Prepare for 0.5.2 release
      * Fix handling of single-paragraph commit message bodies
      * Fix basement detection for empty commit message bodies
      * Support mbox -m to be a maildir
      * man: Update commit url mask to contain 12 chars of ID
      * Fix attestation error messages
      * Deal with [PATCHvX] subjects
      * Fix crash when -c used with incomplete series
      * man: Drop the apostrophe from the linkmask configuration
      * Fix crash with unbalanced [] in subject
      * Fix regression with oddball charsets
      * Up the version to 0.5.2-dev
      * Prepare for 0.5.1 release
      * Fix mbox naming inconsistencies
      * Output less confusing trailer mismatch messages
      * Fix bug with threading when cover ref is missing
      * Fix body part parsing when '---' is not used
      * Use proper c