Xcode project: Compile Lua with OS X options

Avoids some warnings, more secure
Xcode project: set OS X deployment target

… to 10.8 for release builds. This avoids a problem with the change of
default standard libraries from OS X 10.8 to 10.9 and permits using the
default SDK for the given OS X version.
Xcode project: mark Wesnoth not high-resolution capable

Greatly improves performance on retina devices
Xcode project: Remove references to unused flag

ENABLE_OPENMP_SUPPORT: Not available in clang, gcc support unstable in
versions available in Xcode. Defaults to no.
 Micro AIs: clean up loading of Lua files

Consistently use wesnoth.require, avoid wesnoth.dofile. Move commands
as close to beginning of file as possible in order to facilitate custom
modifications of MAIs.
Micro AIs: one more wesnoth.dofile -> wesnoth.require
Update changelogs
fix whitespace
fixup idle loop

(this is probably a bugfix independent of the purpose of this branch)
fix networked idle loop

somehow this was not implemented...
create "fight_on_without_leader" field of [side]

this field is intended to allow battles to continue after the death of a leader
if a side has this flag enabled and any units alive, they will be considered
to have a leader regardless of canrecruit.
add debugging output

help to determine victory conditions associated to victory_when_enemies_defeated
refactor check_victory, don't use [side] no_leader attribute

1. sides without leaders aren't defeated if
"fight_on_without_leader = true". don't use no_leader
for this purpose anymore.
2. refactor to use a std::set instead of std::vector,
and some related improvements, for what was formerly
the "seen_leaders" data structure
[side_drop] sides go to idle, not human (fix bug 21459)

since idle sides don't get initialized until someone takes control
this alleviates 21459. it might possibly aggravate 21397, if that
bug is not fixed by correcting save files with unintialized sides
update changelog
fixup maybe_do_init_side

maybe_do_init_side now does a reality check that the side we are
considering to init actually matches the currently playing side.
it is believed that failure to do such check underlies
bug #21459