Merge branch 'tg/fetch-prune-exit-code-fix'

When "git fetch --prune" failed to prune the refs it wanted to
prune, the command issued error messages but exited with exit
status 0, which has been corrected.

* tg/fetch-prune-exit-code-fix:
  fetch --prune: exit with error if pruning fails

diff --cc builtin/fetch.c
Simple merge