Remove duplicate code from the priest promotion function, consolidate

the code to change one monster type into another into its own function, and use it. The code handling net trapping should probably be somewhere else, though.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@3772 c06c8d41-db1a-0410-9941-cceddc491573

Created by  dolorous  on March 20, 2008
USSKCWQTF6BTE3SFLQVCT6RZHU2R7URWFC7EPO2EN3Z6U4IEQ7GQC
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