bindings: accept "q" and "x" to exit from help viewer and file browser

"Q" is a pretty standard key to exit from something, and "X" is fairly
mnemonic -- better than "E" at least.

src/browser.c

@@ -467,6 +467,10 @@ functionptrtype parse_browser_input(int *kbinput)
 		return do_help_void;
 	    case 'E':
 	    case 'e':
+	    case 'Q':
+	    case 'q':
+	    case 'X':
+	    case 'x':
 		return do_exit;
 	    case 'G':
 	    case 'g':

src/help.c

@@ -486,6 +486,10 @@ functionptrtype parse_help_input(int *kbinput)
 		return do_page_up;
 	    case 'E':
 	    case 'e':
+	    case 'Q':
+	    case 'q':
+	    case 'X':
+	    case 'x':
 		return do_exit;
 	}
     }