Merge branch 'ao/config-from-gitmodules'

Tighten the API to make it harder to misuse in-tree .gitmodules
file, even though it shares the same syntax with configuration
files, to read random configuration items from it.

* ao/config-from-gitmodules:
submodule-config: reuse config_from_gitmodules in repo_read_gitmodules
submodule-config: pass repository as argument to config_from_gitmodules
submodule-config: make 'config_from_gitmodules' private
submodule-config: add helper to get 'update-clone' config from .gitmodules
submodule-config: add helper function to get 'fetch' config from .gitmodules
config: move config_from_gitmodules to submodule-config.c

diff --cc builtin/fetch.c
Simple merge

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

diff --cc config.c
Simple merge

diff --cc submodule-config.c
Simple merge