Bloom filter collator npe fix

Fixed up.
The operator assembler assumed that the loader stream could only be an index scan, in this case it was a project on top of the index scan.  Now the BloomFilter depends on the rowtype of the input stream instead of an exact operator
A PostgresServerBloomFilterIT has been added to test this
Since there is a real change below, minor style nit: constants are generally named ALL_CAPS and marked as `private static final`.