Fix misuse of prefix_path()

When DEFAULT_GIT_TEMPLATE_DIR is specified as a relative path,
init-db made it relative to exec_path using prefix_path(), which
is wrong.  prefix_path() is about a file inside the work tree.
There was a similar misuse in config.c that takes relative
ETC_GITCONFIG path. Noticed by Junio C Hamano.

We concatenate the paths manually. (prefix_filename() won't do
because it expects a prefix with a trailing '/'.)
Signed-off-by: NJohannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin-init-db.c

@@ -141,8 +141,9 @@ static void copy_templates(const char *git_dir, int len, const char *template_di
 		 */
 		template_dir = DEFAULT_GIT_TEMPLATE_DIR;
 		if (!is_absolute_path(template_dir)) {
-			const char *exec_path = git_exec_path();
-			template_dir = prefix_filename(exec_path, strlen(exec_path), template_dir);
+			struct strbuf d = STRBUF_INIT;
+			strbuf_addf(&d, "%s/%s", git_exec_path(), template_dir);
+			template_dir = strbuf_detach(&d, NULL);
 		}
 	}
 	strcpy(template_path, template_dir);

config.c

@@ -484,10 +484,9 @@ const char *git_etc_gitconfig(void)
 		system_wide = ETC_GITCONFIG;
 		if (!is_absolute_path(system_wide)) {
 			/* interpret path relative to exec-dir */
-			const char *exec_path = git_exec_path();
-			system_wide = strdup(prefix_filename(exec_path,
-							     strlen(exec_path),
-							     system_wide));
+			struct strbuf d = STRBUF_INIT;
+			strbuf_addf(&d, "%s/%s", git_exec_path(), system_wide);
+			system_wide = strbuf_detach(&d, NULL);
 		}
 	}
 	return system_wide;