Merge branch 'sb/submodule-helper-clone-regression-fix' into maint

A partial rewrite of "git submodule" in the 2.7 timeframe changed
the way the gitdir: pointer in the submodules point at the real
repository location to use absolute paths by accident.  This has
been corrected.

* sb/submodule-helper-clone-regression-fix:
  submodule--helper, module_clone: catch fprintf failure
  submodule--helper: do not borrow absolute_path() result for too long
  submodule--helper, module_clone: always operate on absolute paths
  submodule--helper clone: create the submodule path just once
  submodule--helper: fix potential NULL-dereference
  recursive submodules: test for relative paths

diff --cc builtin/submodule--helper.c
Simple merge

diff --cc t/t7400-submodule-basic.sh
Simple merge