config.c: remove static keyword from git_env_bool()

Since this function is the preferred way to handle boolean environment
variables it's useful to have it available to other files.
Signed-off-by: NLars R. Damerow <lars@pixar.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

cache.h

@@ -949,6 +949,7 @@ extern int git_config_set_multivar(const char *, const char *, const char *, int
 extern int git_config_rename_section(const char *, const char *);
 extern const char *git_etc_gitconfig(void);
 extern int check_repository_format_version(const char *var, const char *value, void *cb);
+extern int git_env_bool(const char *, int);
 extern int git_config_system(void);
 extern int git_config_global(void);
 extern int config_error_nonbool(const char *);

config.c

@@ -683,7 +683,7 @@ const char *git_etc_gitconfig(void)
 	return system_wide;
 }
 
-static int git_env_bool(const char *k, int def)
+int git_env_bool(const char *k, int def)
 {
 	const char *v = getenv(k);
 	return v ? git_config_bool(k, v) : def;