where does version numberin xx.pc get set ?

[Rod Butcher <rbutcher hyenainternet com>]

Can somebody tell me where I set the version number so it will appear in 
the xxx.pc file ? I've looked at gal.pc.in file and it specifies 
Version: @VERSION@ - that becomes 2.5.0 in  gal.pc - how does it get there ?
Better still, could somebody point me to some doco on how this xxx.pc 
stuff works ?
flame defence - warning, newbie about.
thanks
Rod
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