lazily load core.sharedrepository

The "shared_repository" config is loaded as part of
check_repository_format_version, but it's not quite like the
other values we check there. Something like
core.repositoryformatversion only makes sense in per-repo
config, but core.sharedrepository can be set in a per-user
config (e.g., to make all "git init" invocations shared by
default).

So it would make more sense as part of git_default_config.
Commit 457f06d6 (Introduce core.sharedrepository, 2005-12-22)
says:

  [...]the config variable is set in the function which
  checks the repository format. If this were done in
  git_default_config instead, a lot of programs would need
  to be modified to call git_config(git_default_config)
  first.

This is still the case today, but we have one extra trick up
our sleeve. Now that we have the git_configset
infrastructure, it's not so expensive for us to ask for a
single value. So we can simply lazy-load it on demand.

This should be OK to do in general. There are some problems
with loading config before setup_git_directory() is called,
but we shouldn't be accessing the value before then (if we
were, then it would already be broken, as the variable would
not have been set by check_repository_format_version!). The
trickiest caller is git-init, but it handles the values
manually itself.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

environment.c

@@ -326,13 +326,22 @@ const char *get_commit_output_encoding(void)
 }
 
 static int the_shared_repository = PERM_UMASK;
+static int need_shared_repository_from_config = 1;
 
 void set_shared_repository(int value)
 {
 	the_shared_repository = value;
+	need_shared_repository_from_config = 0;
 }
 
 int get_shared_repository(void)
 {
+	if (need_shared_repository_from_config) {
+		const char *var = "core.sharedrepository";
+		const char *value;
+		if (!git_config_get_value(var, &value))
+			the_shared_repository = git_config_perm(var, value);
+		need_shared_repository_from_config = 0;
+	}
 	return the_shared_repository;
 }

setup.c

@@ -376,8 +376,6 @@ static int check_repo_format(const char *var, const char *value, void *cb)
 
 	if (strcmp(var, "core.repositoryformatversion") == 0)
 		repository_format_version = git_config_int(var, value);
-	else if (strcmp(var, "core.sharedrepository") == 0)
-		set_shared_repository(git_config_perm(var, value));
 	else if (skip_prefix(var, "extensions.", &ext)) {
 		/*
 		 * record any known extensions here; otherwise,