DERBY-532 Support deferrable constraints

A patch ("derby-532-fix-metadata-1") that fixes broken database
metadata for deferred constraint indexes: the metadata query used the
method IndexDescriptor#isUnique to determine logical uniqueness, but
it really represents physical uniqueness now. For deferred unique
constraints, the method that should be used is
"isUniqueDeferrable". Added a test, and also added client/server run
of the regression test for deferred constraints.

Before the fix, the added test fixture "testDatabaseMetaData" failed
in that the index in question was identified as non unique, but it is
logically unique and so should be reported as such.



git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1550113 13f79535-47bb-0310-9956-ffa450edef68