tweaks: put unshifted shortcuts ^6 and M-6 first, instead of ^^ and M-^

The unshifted shortcuts are easier to type, and also less confusing in
my eyes.  Putting them first means they get shown in the help lines,
and get listed first in the ^G help text.

(I would also like to put ^- first instead of ^_ (because the latter
is hard to see when using the default inverse video for shortcuts),
but on several terminal emulators Ctrl+- reduces the font size.)

src/global.c

@@ -1085,11 +1085,12 @@ void shortcut_init(void)
     add_to_sclist(MMAIN|MBROWSER, "F16", 0, do_research, 0);
 #ifndef NANO_TINY
     add_to_sclist(MMAIN, "M-]", 0, do_find_bracket, 0);
-    add_to_sclist(MMAIN, "^^", 0, do_mark, 0);
+    add_to_sclist(MMAIN, "^6", 0, do_mark, 0);
     add_to_sclist(MMAIN, "M-A", 0, do_mark, 0);
     add_to_sclist(MMAIN, "F15", 0, do_mark, 0);
-    add_to_sclist(MMAIN, "M-^", 0, do_copy_text, 0);
+    add_to_sclist(MMAIN, "^^", 0, do_mark, 0);
     add_to_sclist(MMAIN, "M-6", 0, do_copy_text, 0);
+    add_to_sclist(MMAIN, "M-^", 0, do_copy_text, 0);
     add_to_sclist(MMAIN, "M-}", 0, do_indent_void, 0);
     add_to_sclist(MMAIN, "M-{", 0, do_unindent, 0);
     add_to_sclist(MMAIN, "M-U", 0, do_undo, 0);