Use BIGINT instead of INT for key columns.

On TPCH 1TB scale facts and larger key columns overflow when INT is
used, so use 64BIT BIGINT instead.

According to the TPCH spec:
Comment: A common implementation of this datatype will be an integer.
However, for SF greater than 300 some
column values will exceed the range of integer values supported by a
4-byte integer. A test sponsor may use some
other datatype such as 8-byte integer, decimal or character string to
implement the identifier datatype;
Merge pull request #1 from ttmahdy/master

Use BIGINT instead of INT for key columns.