Merge branch 'lf/ref-is-hidden-namespace'

Extend transfer.hideRefs to work better with use of namespaces.

* lf/ref-is-hidden-namespace:
  t5509: add basic tests for hideRefs
  hideRefs: add support for matching full refs
  upload-pack: strip refs before calling ref_is_hidden()
  config.txt: document the semantics of hideRefs with namespaces