give a better error message.

when a player leaves a mp game during a lua call and the other player
pressed escape, lua catches the error that should exit the game, idk
wether i can fix that but at least i can give a better error message.
use rand() instead of get_random() for side shuffle

1) i think it's better to use a simple rand function for things that are
never synced, because everyone knows that rand() isn't synced.
2) my plan is to delete the get_random() function.
fixes wrong side during end turn events in replay
serverside code for the new rng.

i might have to change this code again because the following might be
true: 'instead of checking wether we already gave a random seed it'd
would be better to accept only seed requests ffrom the currently active
side'
use the new synced_context system

the main intention of that patch is to fix gna.org/bugs/?20871,
gna.org/bugs/?21697, some OOS erros related to use of multiple
[get_global_variable] with different sides in one event.
To remove the deterministic random for traits and similar as discusssed
here http://forums.wesnoth.org/viewtopic.php?f=6&t=39611. And to sync
start end prestart events.

this patch unifies how side commands (like attack, recruit, ...) are
executed, during human turn, replay or ai turn by makeing them al call
the same function scned_context::run_in_scned_context.
We also use the new random generator which is automaticly synced during
the execution of scned_context::run_in_scned_context, and otherwise not.
So we cannot cause oos anymore by using rand= from an unsnced command
like "select"
Alternativeley we can also set the new random synced by using the new
RAII object set_sconext_sycned, this happens for example during prestart
events.
Unlike the old random generator, the new random generator is not
determinstic by default because it asks the server (or itself in a SP
game) for a new seed, at every side command (attack, move, recruit ...)
that requires random ,similar to how the previous rand for attacks
worked (it doesnt ask at the beginning, just the first time it is needed
unlinke how attacks worked before). That way we can also unify the rng
for attacks and for other random choices.

this commit breaks ai's advancement aspects, but form what i have heared
that should be fixable.
this commit might create some unused code, that shall be cleared,
especialy i want to remove random.hpp/cpp, rng.hpp/cpp
this commit might contain spelling mistakes.
adding wesnoth.is_synced() #21697
fix a bug when players leave in mp.

as pointed out by EliDupree:
http://www.wesnoth.org/irclogs/2014/03/%23wesnoth-dev.2014-03-19.log
fix a oos bug on sighed enemy units in mp.

movements is still treated specialy and doesn't use
run_in_synced_context by default, because some funtions use the return
value of move_unit.
fix a mp bug

it might happen that we land in playmp_controller::play_side but still
have data in the replay that we recieved from network earlier.

this commit also contains small code cleanups.
change the way the server accepts require_random

removed has_given_random_seed_.
ignore end_turn_exception from get_user_choice

also removes some usless code from persist_var, that was already moved
to get_user_choice.

also adds some logs in do_replay_handle
sync end turn events normally

i hesitated to sync end turn events before, because from the server side
of view every action need a clear defined side assiciated to it, from
wich it accepts [require_new_random].
but now i think the server just associates side 1, that means the new
side after the side turn to the action.

this patch also contains some oos error checks,
remove side check for require_random

I move this check from the server to the client to fix a possible OOS:
to reproduce:

[event]
name = "turn end"
[set_variable]
name=v1
rand= "1..8"
[/set_variable]
[/event]
[event]
name = "moveto"
[message]
side_for=2
message="adfsd"
[/message]
[set_variable]
name=v2
rand= "1..8"
[/set_variable]
[/event]

Do the following: (in a 2p scenario, with no hidden sides):
1) move side 1 leader
2) ignore the message on side 2
3) click end turn on side 1
4) then click on the message on side 2.
5) ->>OOS.

the reason is, the when the rand for v2 is executed on side 1 the
current_side on the  server is side 1 and when rand for v2 is executed
on side 2 the serversided current_side is side 2 => the server accepted
both require_random
fix comments in synced_context.hpp
fix whitespace and remove comment
fix comments in synced_context.cpp
fix an OOS

by moving the code that determines 'which client sends the require_random package to the server' to the client
this commit fixed the following bug (together with another serversided commit):
to reproduce:

[event]
name = "turn end"
[set_variable]
name=v1
rand= "1..8"
[/set_variable]
[/event]
[event]
name = "moveto"
[message]
side_for=2
message="adfsd"
[/message]
[set_variable]
name=v2
rand= "1..8"
[/set_variable]
[/event]

Do the following: (in a 2p scenario, with no hidden sides):
1) move side 1 leader
2) ignore the message on side 2
3) click end turn on side 1
4) then click on the message on side 2.
5) ->>OOS.

the reason is, the when the rand for v2 is executed on side 1 the
current_side on the  server is side 1 and when rand for v2 is executed
on side 2 the serversided current_side is side 2 => the server accepted
both require_random

this bug fixed that by moving the decision which side should send the
require_random to the clients.

this commit might contain spelling corrections.
comment changes/corrections
removed unused rng code.

i also replaced set_random_results/get_random_results with
synced_checkup in recruit_checksums in create.cpp.

i don't see a reason why we shouldn't use the checkup when calling
place_recruit from wml, since the wml is called on all clients. Just
like a normal recruit. (if we are in an unsynced context then checkup
doesnt have any effect anyway.)
move get_random_calls()

from synced_rng to rng.