A branch compatible with Apache Impala (incubating) 2.8.0

Works with Apache Impala (incubating) 2.7.0

Codegen improvements

Change-Id: I3d2d2e7e9f970dda8ccb4e729fdbfbdeb1dd9a06

Allow UDFs in conjunct expressions.

Change-Id: Ie205c8cd6b35117311f0aab58b9170109c07082f

IMPALA-525: Sequence scanners use average block size to minimize read…

…s past eosr

Change-Id: I33c198a5958ca8110f67682f7d51cfaf55b0bbd6

Updates from more ScanNode cleanup.

Update for codegen.