Promotion by Technology

[fatherbushido]

Promotion component have a RequiredXP element. That one is a non negative integer. Currently we can use a tech to replace it by 0.

The effect of setting RequiredXP to 0 is :

1. promote the current units (see Promotion) (with entity mod)
2. construct the (more) promoted unit instead of the original unit (ref r14388) (with template mod)

That is used to promote a unit with a tech (see for example mace_champion_infantry_a to mace_champion_infantry_e).

But that is not fully flexible : for example one can perhaps want :

• that unit never promote with xp (see old ugly workaround with a 99999 requiredXP
• allow a promotion only when a given tech is researched