Add "const" qualifier to "char *editor_program".

Also use "git_config_string" to simplify "config.c" code
where "editor_program" is set.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

cache.h

@@ -614,7 +614,7 @@ extern const char *pager_program;
 extern int pager_in_use(void);
 extern int pager_use_color;
 
-extern char *editor_program;
+extern const char *editor_program;
 extern char *excludes_file;
 
 /* base85 */

config.c

@@ -443,12 +443,8 @@ int git_default_config(const char *var, const char *value)
 	if (!strcmp(var, "core.pager"))
 		return git_config_string(&pager_program, var, value);
 
-	if (!strcmp(var, "core.editor")) {
-		if (!value)
-			return config_error_nonbool(var);
-		editor_program = xstrdup(value);
-		return 0;
-	}
+	if (!strcmp(var, "core.editor"))
+		return git_config_string(&editor_program, var, value);
 
 	if (!strcmp(var, "core.excludesfile")) {
 		if (!value)

environment.c

@@ -32,7 +32,7 @@ size_t packed_git_limit = DEFAULT_PACKED_GIT_LIMIT;
 size_t delta_base_cache_limit = 16 * 1024 * 1024;
 const char *pager_program;
 int pager_use_color = 1;
-char *editor_program;
+const char *editor_program;
 char *excludes_file;
 int auto_crlf = 0;	/* 1: both ways, -1: only when adding git objects */
 unsigned whitespace_rule_cfg = WS_DEFAULT_RULE;