Merge branch 'minor'

* minor:
  sync: update third-part files from upstream
  maint: fix typo in error message of a maintainer-only rule
  maint: bump version number 1.15 -> 1.15a ('minor' Git branch)
  release: stable minor release 1.15
  NEWS: minor improvements and fixed some typos and grammaros

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>

diff --cc NEWS
Simple merge