DERBY-6693 Assert failure/ArrayIndexOutOfBoundsException when using COUNT in MERGE matching clause

Patch derby-6693 which forbids aggregates in the matching clauses, and
adds a test case to MergeStatementTest, but:
the checked in code using assertCompileError instead of
assertStatementError for more precision (in MergeStatementTest).

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1616523 13f79535-47bb-0310-9956-ffa450edef68