Refactoring unit class to use boost::scoped_ptr instead of raw pointer.

This change aims to simplify the code, making the intents more explicit.
There wasn't a memory leak in the previous version, but it could easily be
introduced in the future.

Also, RAII is part of the coding standards of Wesnoth, as noted in the wiki.

There are other raw pointers in the unit class, but unit don't own them, then
I leave them unchanged.
Code cleanup and mark none core items.
Use proper variable name.
Optipng run

  Original size: 444 KiB on 301 files
 Optimized size: 137 KiB
   Total saving: 306 KiB = 69% decrease
"Transition *u*pdate" ---> "Transition *U*pdate"
New portraits for delfador, asheviere, and moremirmu in HttT.
New portrait for old-delfador in delfador's memoirs.
New portrait for old-delfador in tutorial.
merged the tools + tools options palettes in the editor theme artwork
revised slicing for the 800x600 editor theme
Add some missing sources to CMake. Fabi owes me a cookie.
New playlist FULL_MUSIC_PLAYLIST, containing all tracks.
Macro documentation for FULL_MUSIC_PLAYLIST.
Merge pull request #5
Merge branch 'master' of github.com:wesnoth/wesnoth-old
Made the gui1 scrollbar make use of the pressed images.
gui1 scrollbar uses the new arrow icon overlays.
Made use of lipkab's new full playlist.
Possibly fixed a bug with uninitialized translated wml attributes.
Fixed incorrect behaviour of "Shuffle sides" in MP.