Added a message when trying to look at the beam path of a spell that doesn't need one. (AFAIK, it's only spells that have this behaviour. Should this not be the case, or should this ever change, the message will have to be adapted.)
git-svn-id: https://crawl-ref.svn.sourceforge.net/svnroot/crawl-ref/trunk@2093 c06c8d41-db1a-0410-9941-cceddc491573
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