Merge branch 'ab/fetch-prune'

Merge branch 'ab/fetch-prune'

Clarify how configured fetch refspecs interact with the "--prune"
option of "git fetch", and also add a handy short-hand for getting
rid of stale tags that are locally held.

* ab/fetch-prune:
  fetch: make the --prune-tags work with <url>
  fetch: add a --prune-tags option and fetch.pruneTags config
  fetch tests: add scaffolding for the new fetch.pruneTags
  git-fetch & config doc: link to the new PRUNING section
  git remote doc: correct dangerous lies about what prune does
  git fetch doc: add a new section to explain the ins & outs of pruning
  fetch tests: fetch <url> <spec> as well as fetch [<remote>]
  fetch tests: expand case/esac for later change
  fetch tests: double quote a variable for interpolation
  fetch tests: test --prune and refspec interaction
  fetch tests: add a tag to be deleted to the pruning tests
  fetch tests: re-arrange arguments for future readability
  fetch tests: refactor in preparation for testing tag pruning
  remote: add a macro for "refs/tags/*:refs/tags/*"
  fetch: stop accessing "remote" variable indirectly
  fetch: trivially refactor assignment to ref_nr
  fetch: don't redundantly NULL something calloc() gave us