Merge branch 'ds/log-exclude-decoration-config'

Merge branch 'ds/log-exclude-decoration-config'

The "--decorate-refs" and "--decorate-refs-exclude" options "git
log" takes have learned a companion configuration variable
log.excludeDecoration that sits at the lowest priority in the
family.

* ds/log-exclude-decoration-config:
  log: add log.excludeDecoration config option
  log-tree: make ref_filter_match() a helper method