Changed the rules for plot improvement which require bonuses.

For the purpose of building plot improvements such as railroads, all
resources available to a city are now provided to all the workable plots
around that city.

The purpose of this change is to let civs use Standard Ethonol corp to
build railroads.
In AI_techValue, the random bonus for wonders now depends on personlaity

The value of bEnablesWonder is now proportional to the leader's
"iWonderConstructRand" value, and the average total value from this is
significantly lower than before.
CvCity::foodDifference now has bIgnoreProduction as an optional argument

This argument is used when we care only about how much food the city
would normally be gaining, not how much it is currently gaining.
eg. when evaluting units & buildings.
CvCity & CvPlayer::canConstruct now has an optional bIgnoreTech argument

This will be used in the rewrite of CvPlayerAI::AI_techBuildingValue.
Implemented an all new version of CvPlayerAI::AI_techBuildingValue.

The new function uses CvCityAI::AI_buildingValue to estimate the value
of each building in a subset of the player's cities. This value is
scaled based on the production cost of the building, and a few other
factors.

The old version of AI_techBuildingValue has been renamed to
AI_techBuildingValue_old and left intact for comparison purposes. It
will be removed at some later time.

(The following comment currently appears in the source code.)

--
The original code had some vague / ad-hoc calculations to evalute the
buildings enabled by techs. It was completely separate from
CvCity::AI_buildingValue, and it ignored _most_ building functionality.
I've decided it would be better to use the thorough calculations already
present in AI_buildingValue. This should make the AI a bit smarter, and
the code more easy to update. But it might run slightly slower.

Note: There are some cases where this new kind of evaluation is
significantly flawed. For example, Assembly Line enables factories and
coal power plants; since these two buildings are highly dependant on one
another, their individual evaluation will greatly undervalue them.
Another example: catherals can't be built in every city, but this
function will evaluate them as if they could, thus overvaluing them. But
still, the original code was far worse - so I think I'll just tolerate
such flaws for now.
--
Made some adjustments the AI's espionage evaluations.

Increased the value of spread culture and allowed it to be used for
offence as well as defence.

Redesigned the sabortage building calculation.

Added a temporary assert to CvUnitAI::AI_bestPlotEspionage to check if
'espionage economy' is being misused.
Simplified the implementation of AI_isDoVictoryStrategyLevel3 & 4.

All of the victory types are now checked in a single test rater than
tested individually. The functionality is unchanged but it may be
slightly faster.
Improved the stateReligionCommerce part in CvCityAI::AI_buildingValue.

The evaluation now counts the actual number of religious buildings
affected by the bonus rather than just counting how many cities the
religion is in. Also, the average commerce multiplier is applied (rather
than no multiplier at all).
Redesigned the iSlowValue scaling in CvUnitAI::AI_greatPersonMove.

The new version uses a modifer calculated from the personality &
situation of the player.
AI_buildingValue no longer uses iPriorityFactor for special buildings.

If the building's production cost is non-positive, the modifier is not
applied. This means buildings such as academies will not be affected.
Food added by the Volcano event is now reported by 'Event Signs'.
Tweaked the AI evaluation of space-race techs.

AI's aiming for a space victory will now prefer tech which unlock
spaceship parts which they can build more than one of.
Made some adjustments to AI_targetCityValue.

Newly founded (autoraze) cities are now given 1/3 of their normal value.
Increased the bounty on cities which are part of an imminent victory.
Added some situational nuance to the wonder bonus in AI_techValue.
Made a minor tweak to AI_getCityImportance and added some comments.
Made lots of changes to CvCityAI::AI_cityThreat.

The threat value calculation for each player is now broken down into two
factors: iAccessFactor and iCivFactor. iAccessFactor now includes a
(very rough) naval assault calculation. Some adjustments related to
iCivFactor have been tweaked.

Also, at the end of the calculation there is now a iImportanceFactor
calculation which multiplies the total threat level based on special
factors for this city. eg. cities that are vital parts of the civ's
victory strategy are considered to be very important, and civs with
active world wonders have some added importance.
Reduced some happiness effects in AI_buildingValue.

Commerce happiness (eg. theatres) was being over-estimated, and double
counted; and war-weariness reduction was similar, but not quite so bad.
Both have been reduced.
Adjusted the production 'scale' effect in AI_techBuildingValue.

Buildings with cost below the scale can now increase the building's
value (up to a factor of 3).

The scale multiplier for wonders now depends on map size & city count.
Made some more tweaks to CvPlayerAI::AI_espionageVal.

Increased the value of sabotaging projects.
Reduced the value of spreading unhappiness.
Reduced the value of sabotaging buildings.

Disabled sabotage completely when the city is in disorder (not for any
strategy reason, but just because the current evaluation may give wildly
inaccurate results if the city is in disorder - sometimes too high, and
sometimes too low.)
Added a new condition to isMaliciousEspionageTarget, and added AI prefix

CvPlayerAI::AI_isMaliciousEspionageTarget now returns true if this
player and the target are both using stage4 victory strategies.
(Unless the player is aiming for a diplomacy victory.)