git push recurse.submodules behavior changed in 2.13

Hi all,

It looks like the git push recurse-submodules behavior has changed.
Currently with 2.13 you cannot run "git push
--recurse-submodules=on-demand" if the parent repo is on a different
branch than the sub repos, e.g. parent repo is on "develop" and
sub-repo on "master". I created a test that can be found here [1].

A bisect shows that the change to propagate refspec [2] to the
submodules is the culprit. imho this is an undesired change in
behavior. I looked at the code but couldn't see an easy way to fix
this issue without breaking the feature mentioned above. The only
option I can think of is to control the refspec propagation behavior
using a flag, e.g. "--propagate-refspecs" or add another
recurse-submodules option, e.g. "--recurse-submodules=propagate"

What do you all think ?

[1] https://gist.github.com/jvshahid/b778702cc3d825c6887d2707e866a9c8
[2] https://github.com/git/git/commit/06bf4ad1db92c32af38e16d9b7f928edbd647780