Change CASE to work with expressions in the THEN clause

[Vlad Merticariu]

The CASE statement only accepts point values in the THEN and ELSE clauses:

CASE WHEN condition THEN pointValue

ELSE pointValue

END

It should be changed to fit expressions as well:

CASE WHEN condition THEN expression

ELSE expression

END

so queries of the following form are accepted:

CASE WHEN c > 0 THEN log©

ELSE 0

END

Whenever an expression is given in the THEN clause, the array input of the operation should be removed and instead a point-by-point execution should be performed. This is necessary for allowing conditional evaluation: log© would fail if evaluated on the entire array, if the array contains points with values ⇐ 0. Cell basis execution ensures that only the points passing the condition in the WHEN statement are considered.