jdorje: Add a new function city_can_use_specialist t...

This is an automated notification of a change to freeciv cvs, 
on Wed Jun  2 15:54:14 PDT 2004 = Wed Jun  2 22:54:14 2004 (GMT)
by Jason Dorje Short <jshort@xxxxxxxxxxxxxx>

---- Files affected:

freeciv/client citydlg_common.c
freeciv/common city.c city.h
freeciv/common/aicore cm.c
freeciv/server cityhand.c

---- Log message:
      Tag: HEAD

Add a new function city_can_use_specialist to check if a specialist type
is usable by a particular city.  Use this function in several places to
more easily check if the specialist is valid.  Also, fix a bug when the
player tries to change specialists in the citydlg.

Patch by me in PR#8882.