BOARD::Add now it's wrapped in python and clears the .thisown flag on python to avoid GC from deleting the object later (BOARD will do)

* dlist.i empty list fixed (Segfault)
* units.i: FromMM FromMils ToMM ToMils
* added a little example (listPcb.py) that shows most items in a board

DLIST iterator code, now we can do:

    for module in pcb.m_Modules:
    	print module.GetReference()

instead of:

    module = pcb.m_Modules

    while module:
	print module.GetReference()
	module = module.Next()

or even:
    module_list = list(pcb.m_Modules)

* Added a first test 'testLoadSave.py'

CMakeLists.txt options to build scripting or scripting modules

It does nothing but loading and initializing right now.

ModEdit (and ModView): make "invisible" texts visible. They are not visible in  the board editor, but must be visible in the footprint editor.
Minor doc update.

* Convert Eeschema from manually linked list to DLIST for storing
  SCH_ITEM objects.
* Add helper functions to SCH_SCREEN for appending list of SCH_ITEM
  objects.
* Fix bug in wire editing code for accurate undo/redo behavior.
* Add member to DLIST to append another DLIST.
* Other minor code cleaning.

Pcbnew: zone filling: fix broken thermal relief shape for oval pads. mainly noticeable for oval pads having very different X and Y sizes.

* Pcbnew: in hight contrast mode the 'V' hotkey did not always refresh the screen.
* Eeschema: incorrect print scale when the option 'Show page limits' is disable.

    derived classes' implementations of these functions become non virtual and
    can be truly _inlined_ for speed!  All GetPosition() in derived classes were also
    changed to return const wxPoint&, that is, a reference rather than a
    full copy of the position wxPoint. There was no need for polymorphism in
    {Get,Set}Position() since we never call these functions via generic pointer.
  * Remove BOARD::{Get,Set}Position() since they were only there to satisfy
    the pure virtuals established in BOARD_ITEM, which are now gone.
  * Added const wxPoint& CPolyLine::GetPos(), made CPolyLine::Get{X,Y}() inline.
  * Derive CPolyPt from wxPoint so we can return "const wxPoint&" fromt
    CPolyLine::GetPos().