Fix file lists getting fed to file triggers multiple times (#370)

A prefix can have arbitrary number of matches within a given header,
but each header should be fed into the file list iteration just once.
Otherwise we end up feeding the same file list over and over to the
scriptlet - hundreds of megs or gigs of waste in worser cases.

(cherry picked from commit e6effe3)

lib/rpmtriggers.c

@@ -327,6 +327,8 @@ static const char *matchFilesNext(matchFilesIter mfi)
 						RPMDBI_DIRNAMES, mfi->pfx, 0);
 
 	    rpmdbFilterIterator(mfi->pi, mfi->tranPkgs, 0);
+	    /* Only walk through each header with matches once */
+	    rpmdbUniqIterator(mfi->pi);
 
 	} while (fx >= 0);