Define externally accessible contants with 'var' instead of 'const'

Just as we did with classes, define other constants that are (or
may be) used from other modules with 'var' to cut down on warnings.

https://bugzilla.gnome.org/show_bug.cgi?id=785084

js/ui/shellMountOperation.js

@@ -18,7 +18,7 @@ const ModalDialog = imports.ui.modalDialog;
 const Params = imports.misc.params;
 const ShellEntry = imports.ui.shellEntry;
 
-const LIST_ITEM_ICON_SIZE = 48;
+var LIST_ITEM_ICON_SIZE = 48;
 
 const REMEMBER_MOUNT_PASSWORD_KEY = 'remember-mount-password';
 
@@ -473,7 +473,7 @@ const GnomeShellMountOpIface = '<node> \
 </interface> \
 </node>';
 
-const ShellMountOperationType = {
+var ShellMountOperationType = {
     NONE: 0,
     ASK_PASSWORD: 1,
     ASK_QUESTION: 2,