index: stage an unregistered submodule as well
index: stage an unregistered submodule as well

We previously added logic to `_add_bypath()` to update a submodule. Go
further and stage the submodule even if it's not registered to behave
like git.

since2014/libgit2,sim0629/libgit2,mrksrm/Mingijura,mrksrm/Mingijura,linquize/libgit2,iankronquist/libgit2,leoyanggit/libgit2,mhp/libgit2,mcanthony/libgit2,sygool/libgit2,jeffhostetler/public_libgit2,dleehr/libgit2,since2014/libgit2,linquize/libgit2,magnus98/TEST,JIghtuse/libgit2,ardumont/libgit2,JIghtuse/libgit2,oaastest/libgit2,sygool/libgit2,stewid/libgit2,yongthecoder/libgit2,magnus98/TEST,iankronquist/libgit2,oaastest/libgit2,yosefhackmon/libgit2,Corillian/libgit2,Corillian/libgit2,saurabhsuniljain/libgit2,ardumont/libgit2,dleehr/libgit2,skabel/manguse,yosefhackmon/libgit2,since2014/libgit2,mhp/libgit2,JIghtuse/libgit2,stewid/libgit2,mhp/libgit2,KTXSoftware/libgit2,mrksrm/Mingijura,yongthecoder/libgit2,ardumont/libgit2,mrksrm/Mingijura,stewid/libgit2,leoyanggit/libgit2,sim0629/libgit2,Tousiph/Demo1,skabel/manguse,skabel/manguse,yongthecoder/libgit2,spraints/libgit2,mcanthony/libgit2,jeffhostetler/public_libgit2,dleehr/libgit2,yosefhackmon/libgit2,stewid/libgit2,KTXSoftware/libgit2,falqas/libgit2,since2014/libgit2,mcanthony/libgit2,jeffhostetler/public_libgit2,yosefhackmon/libgit2,skabel/manguse,yongthecoder/libgit2,Corillian/libgit2,jeffhostetler/public_libgit2,claudelee/libgit2,joshtriplett/libgit2,skabel/manguse,joshtriplett/libgit2,kissthink/libgit2,claudelee/libgit2,claudelee/libgit2,leoyanggit/libgit2,magnus98/TEST,dleehr/libgit2,yongthecoder/libgit2,magnus98/TEST,sygool/libgit2,iankronquist/libgit2,joshtriplett/libgit2,claudelee/libgit2,sim0629/libgit2,yongthecoder/libgit2,kenprice/libgit2,Tousiph/Demo1,mhp/libgit2,sygool/libgit2,joshtriplett/libgit2,saurabhsuniljain/libgit2,claudelee/libgit2,linquize/libgit2,jeffhostetler/public_libgit2,iankronquist/libgit2,linquize/libgit2,sim0629/libgit2,mhp/libgit2,oaastest/libgit2,spraints/libgit2,mcanthony/libgit2,leoyanggit/libgit2,ardumont/libgit2,stewid/libgit2,falqas/libgit2,leoyanggit/libgit2,leoyanggit/libgit2,oaastest/libgit2,spraints/libgit2,KTXSoftware/libgit2,Corillian/libgit2,Tousiph/Demo1,spraints/libgit2,Tousiph/Demo1,dleehr/libgit2,magnus98/TEST,linquize/libgit2,sygool/libgit2,jeffhostetler/public_libgit2,Tousiph/Demo1,spraints/libgit2,Tousiph/Demo1,ardumont/libgit2,kenprice/libgit2,skabel/manguse,KTXSoftware/libgit2,kissthink/libgit2,JIghtuse/libgit2,saurabhsuniljain/libgit2,joshtriplett/libgit2,iankronquist/libgit2,mcanthony/libgit2,kenprice/libgit2,dleehr/libgit2,since2014/libgit2,saurabhsuniljain/libgit2,kissthink/libgit2,oaastest/libgit2,yosefhackmon/libgit2,joshtriplett/libgit2,saurabhsuniljain/libgit2,KTXSoftware/libgit2,Corillian/libgit2,falqas/libgit2,since2014/libgit2,falqas/libgit2,KTXSoftware/libgit2,ardumont/libgit2,Corillian/libgit2,linquize/libgit2,falqas/libgit2,stewid/libgit2,sygool/libgit2,oaastest/libgit2,mrksrm/Mingijura,iankronquist/libgit2,spraints/libgit2,sim0629/libgit2,mhp/libgit2,mrksrm/Mingijura,kissthink/libgit2,mcanthony/libgit2,kissthink/libgit2,falqas/libgit2,JIghtuse/libgit2,kenprice/libgit2,kissthink/libgit2,JIghtuse/libgit2,saurabhsuniljain/libgit2,kenprice/libgit2,magnus98/TEST,kenprice/libgit2,sim0629/libgit2,claudelee/libgit2,yosefhackmon/libgit2