Add foreignKey constraint validation in PG session when creating a table

[johnfangAFW]

As observed in issue: #270, we didn't validate the foreign key constraint properly in pg session. We need to add the support when creating a table so that we could fail the second table creation for the following example:

CREATE TABLE PKTABLE (ptest1 int, ptest2 int, UNIQUE(ptest1, ptest2));
CREATE TABLE FKTABLE_FAIL1 (ftest1 int REFERENCES pktable(ptest1));