Merge branch 'jl/maint-submodule-recurse-fetch' into maint

Merge branch 'jl/maint-submodule-recurse-fetch' into maint

"git fetch" that recurses into submodules on demand did not check if it
needs to go into submodules when non branches (most notably, tags) are
fetched.

By Jens Lehmann
* jl/maint-submodule-recurse-fetch:
  submodules: recursive fetch also checks new tags for submodule commits