Merge branch 'ds/decorate-filter-tweak'

The namespaces used by "log --decorate" from "refs/" hierarchy by
default has been tightened.

* ds/decorate-filter-tweak:
  fetch: use ref_namespaces during prefetch
  maintenance: stop writing log.excludeDecoration
  log: create log.initialDecorationSet=all
  log: add --clear-decorations option
  log: add default decoration filter
  log-tree: use ref_namespaces instead of if/else-if
  refs: use ref_namespaces for replace refs base
  refs: add array of ref namespaces
  t4207: test coloring of grafted decorations
  t4207: modernize test
  refs: allow "HEAD" as decoration filter

cache.h

@@ -1016,7 +1016,6 @@ void reset_shared_repository(void);
  * commands that do not want replace references to be active.
  */
 extern int read_replace_refs;
-extern char *git_replace_ref_base;
 
 /*
  * These values are used to help identify parts of a repository to fsync.