Merge branch 'jk/check-docs-update'

Simplify "make check-docs" implementation and update its coverage. * jk/check-docs-update: check-docs: get documented command list from Makefile check-docs: drop git-help special-case check-docs: list git-gui as a command check-docs: factor out command-list command-list: mention git-credential-* helpers command-list: add git-sh-i18n check-docs: update non-command documentation list check-docs: mention gitweb specially