Merge branch 'ab/credentials-in-url-more'

Merge branch 'ab/credentials-in-url-more'

Rename fetch.credentialsInUrl to transfer.credentialsInUrl as the
single configuration variable should work both in pushing and
fetching.

* ab/credentials-in-url-more:
  transfer doc: move fetch.credentialsInUrl to "transfer" config namespace
  fetch doc: note "pushurl" caveat about "credentialsInUrl", elaborate