[Freeciv-Dev] server crashed upgrading a frigate (PR#6735)

["Jason Short" <jdorje@xxxxxxxxxxxxxxxxxxxxx>]

<URL: http://rt.freeciv.org/Ticket/Display.html?id=6735 >

I like the concept of Raimar's latest patch.  Here's a rework of it:

- I removed upgrade_would_strand.  This function is now unneeded since 
it is a less strict check than the (simpler) one that is done.  (Because 
punit->transported_by is now enforced strictly, we would have to 
actually reassign the units in upgrade_unit if we wanted to do the less 
strict check.)  Also, this is a duplicate of 
ground_unit_transporter_capacity, so this function shouldn't exist in 
any case.

- I renamed unit_upgrade as test_unit_upgrade.  Note that it has no side 
effects now.

- Rather than pass separate need_city and need_gold parameters to 
upgrade_unit and test-unit_upgrade, I just pass a single parameter: 
is_free.  This is TRUE for Leonardo's, FALSE everywhere else.  It allows 
a more understandable interface and a stricter assertion within 
upgrade_unit.

- I do not pass to_unittype to test_unit_upgrade.  Rather, this function 
retrieves the unittype itself and returns UR_NO_UNITTYPE if it's 
invalid.  It would be okay with me if we did pass the unittype in to the 
function (the way I have it now there is potential for error, since the 
unittype used by test_unit_upgrade is generated differently from the one 
the callers are using), but we definitely need to verify this value and 
have a UR_NO_UNITTYPE return value.

- New functiong get_unit_upgrade_info is added to citydlg_common.  This 
makes the GUI code very simple.

- Added support for gui-gtk-2.0, gui-win32, and gui-xaw.  gui-gtk code 
is updated.  gui-sdl is unsupported (but will still work just fine).

- Maybe something else I forgot about.

Tested under some, but not all GUIs.

jason