Update log.
When building expressions using linq4j, use varargs method over iterable method wherever possible.
Progress on code generation for windowed aggregation. Fix 2 bugs in type derivation of windowed aggregates.

Cleanups: call "BigDecimal.valueOf" rather then "new BigDecimal()" whenever possible; migrate an array to an immutable list in SqlTypeStrategies.
Define the ORDER BY key of a window using RelCollation. Make RelCollationImpl immutable.