refugees population bug fixed, thanks Cvv

Immigrants are attracted by happiness and productivity of your empire from foreign cities. Ideologies affect migration in different ways.

What's new in v6:
* migrants carry religion
* part of conquered population escape as refugees
* emigration system reworked: progress bars instead of probabilities

- Updated to work with Brave New World
- One bug fixed when people migrated to unmet civs (thanks doktorstick)

People migrate between cities seeking a better life. Migrants are attracted by happiness, productiveness and policies. Develop your empire and your rival's citizens will leave their homeland for your prosperous country.

English and Russian languages are supported.
Gods and Kings expansion is required.

[color=red]What's new in v 5?[/color]

• local happiness and prosperity indicators added to the city view.
  
• local happiness now factors prosperity.
  
• no emigration to starving cities anymore.
  
• immigration penalty added to the Order policy to make it less powerful.
  
• cooldown period increased to 12 turns.
  
• a major bug resolved which caused CTD.

Mechanics
For each city a prosperity value is calculated each turn. It is composed of empire's happiness, local (city) happiness, number of social policies and productivity. Productivity is a sum of various city's outputs (food, production, faith, great people points etc) divided by number of citizens. The formula is: 0.1 * happiness + 0.1 * localHappiness + 0.2 * productivity + 0.05 * numberOfPolicies. For every city there is a chanse that at the next turn one of its citizens will move to another city which has a higher prosperity value (if such a city exists). This chance depends on the current era and the source city's population. If there are more than one possible destinations for emigration, preference is given to relatively more prosperous and closer cities. For cities of the same civilization distance is not considered so, all other conditions being the same, internal migration is more likely.

Gameplay
Positive happiness matters much more, so balancing at the 0 happines level is not a viable strategy with this mod, as you will begin to lose your citizens to your neightbours. More happiness is better. Infrastructure also factors migration so tall empires get an advantage over less developed wide ones draining their population (especially with all those great people improvements which output is doubled with the Freedom finisher). Main thing here is to get enough happiness to support high-population cities as for a tall empire it is harder to get luxuries.

The best way to magnify the immigration rate is to increase your empire's happiness (1 prosperity point (pp) = 10 happiness). Second effective is ifrastructure development (1 pp = 5 avg output per citizen). And getting more social policies gives you another but quite a small prosperity bonus (1 pp = 20 policies). Exception is for the Freedom: adopting it gives you the whole 1 additional pp. Also, building the Statue of Liberty will help to attract more immigrants from abroad: distance to your cities will not be considered, as if they were migrating inside their own country.

To reduce emigration from your cities adopt Autocracy. This halves emigration probability. Or declare war on your rival: people cant emigrate to empires you are at war with. Order policy is an opposite and has an immigration penalty.

Details and special rules

• Migrations are less likely early in the game because of the era modifiers. Emigration reaches its full strength when you enter the Industrial era. Maximum migration distance also rises with the current era too.
  
• Between two emigration events from one city there is a minimum 12-turn (for the standard speed) span.
  
• Emigration from bigger cities is more likely.
  
• There is no emigration from city-states but emigration to them is possible though is not very likely as they usually have low happiness.
  
• Your cities get -1 pp penalty for being unhappy and -2 pp for being very unhappy.

The mod's discussion thread at civfanatics.com
http://folu.me/Emigration