pass halo::manager as an argument to unit frame redraw fcn
move halo::manager from play_controller to display

Also this removes the need to have it in the editor.
add operators == (attribute_value, std::string)
fixup 'add operators == (attribute_value, std::string)'

we need to keep the code form using these functions in case of c["a"] ==
0
add operators !=(attribute_value, std::string)
fixup use of operator !=(attribute_value, const char*)

since we don't use t_string's == operator anymore in this case, c["a"]
!= "" will evaluate to true in case of "a" beeing not existent. To get
the desired behaviour we need to use the .empty() method.

I also add an assert in map_generation for a possible segfault that i
noticed during fixing this.
fix unit(_type)::resistance_filter_matches

fix use of operator == (atribute_value, char*)
extend attibute_value unit test
add display chat manager, notifications support outside game_display

The functionality of tracking observers and displaying chat messages
is moved to a manager class, which the gui owns.

The functionality of displaying notifications is similarly moved out
of the game_display and to a private namespace. (Static singleton
pattern seems okay here since there really won't need to be more
than one of these for a single application, it seems.)
Merge pull request #226 from gfgtdf/config_comparision

add operators ==,!= (attribute_value, std::string)

previously comparisions like c["a"] = "b" were evaluated by 
inline bool operator==(const std::string &a, const t_string &b) 
by casting atribute_value to std::string, and const char * to t_string

we fix this by adding explicit equality operator for these cases.

Not creating t_string also results in significant preformance improvements in some cases.
fixup SDL2 compilation
Merge branch 'master' of git://github.com/wesnoth/wesnoth
move bar drawing code from display to unit_drawer

That's the only place it is used.
fixup SDL2 notifications

fixes up series of commits:
cb5a9a0d28ed4761272fcad65001c376445cc7d6
fafb03bafb72b16572e2a794fbd0210879c8d26f
move notifications files to their own folder
cleanup notifications preprocessor instructions, for readability
move some utility files to utils folder
Resort CodeBlocks project file
Resort wesnoth-main_SRC in CMakeLists.txt
Readd copyright notices

Apparently lost in commit cb5a9a0d28ed4761272fcad65001c376445cc7d6.