Let a level_id be directly compared to a branch type with == and != to

determine if a level_id is (not) in BRANCH_FOO; takes care of comparing level_type to LEVEL_DUNGEON.

git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@6034 c06c8d41-db1a-0410-9941-cceddc491573

Created by  zelgadis  on June 21, 2008
Q2AYZGR7UBWG4CKVR6PJQD3UHDEBMAFBQ5PZLHT64CTREG3JYFZAC
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