Merge branch 'jk/submodule-c-credential'

An earlier addition of "sanitize_submodule_env" with 14111fc4 (git:
submodule honor -c credential.* from command line, 2016-02-29)
turned out to be a convoluted no-op; implement what it wanted to do
correctly, and stop filtering settings given via "git -c var=val".

* jk/submodule-c-credential:
  submodule: stop sanitizing config options
  submodule: use prepare_submodule_repo_env consistently
  submodule--helper: move config-sanitizing to submodule.c
  submodule: export sanitized GIT_CONFIG_PARAMETERS
  t5550: break submodule config test into multiple sub-tests
  t5550: fix typo in $HTTPD_URL

git-submodule.sh

@@ -124,9 +124,10 @@ isnumber()
 # of the settings from GIT_CONFIG_PARAMETERS.
 sanitize_submodule_env()
 {
-	sanitized_config=$(git submodule--helper sanitize-config)
+	save_config=$GIT_CONFIG_PARAMETERS
 	clear_local_git_env
-	GIT_CONFIG_PARAMETERS=$sanitized_config
+	GIT_CONFIG_PARAMETERS=$save_config
+	export GIT_CONFIG_PARAMETERS
 }
 
 #