[lazarus] Enable/CheckMenuItem

[Micha Nelissen]

Hi,

Specification of Enable/CheckMenuItem needs to be more specific. Due to 
  win32api obscurities it needs to be changed: note that only hndMenu 
changed:

hndMenu: specifies _parent_ of menuitem to change
uIDEnableItem: Integer - menu item to check/uncheck
bChecked: Boolean      - new state of the menu item

Mattias, please fix the gtk to fit the new specification.

Micha.