Set script.lang in the environment to either 'forth' or 'simple' to

reflect what scripting language was compiled into the loader. I
anticipate that being able to find this out quickly from the OK prompt
will be useful in troubleshooting in the future.

stand/common/interp_forth.c

@@ -337,6 +337,7 @@ void
 interp_init(void)
 {
 
+	setenv("script.lang", "forth", 1);
 	bf_init();
 	/* Read our default configuration. */
 	interp_include("/boot/loader.rc");

stand/common/interp_simple.c

@@ -39,6 +39,7 @@ void
 interp_init(void)
 {
 
+	setenv("script.lang", "simple", 1);
 	/* Read our default configuration. */
 	interp_include("/boot/loader.rc");
 }