merge MMcM: Do not pass length from SQL type to LONGVARBINARY.

Merge pull request #1168 from MMcM/sql-layer/long-varbinary-no-length-from-sql
https://github.com/FoundationDB/sql-layer/pull/1168
merge MMcM: Move more function implementations into common

Merge pull request #1169 from MMcM/sql-layer/more-common-funcs
https://github.com/FoundationDB/sql-layer/pull/1169
ColumnTypeString.
DescribeExpression.
IfNull.
No arg funcs.
Pad.
Repeat.
SequenceValue.
SerialSequence.
Substring.
TBinary.
TParsers.