SINGLE function can be used to return first value from a dynamic array result, or to return the value of the cell which matches the current row (VALUE error if not match) for a range. Excel allows you to specify an at-sign unary operator rather than SINGLE function; this PR does not permit that.
Add support for reading CSE array functions for Gnumeric.
Throw an exception if setValueExplicit Formula is invalid (not a string, or doesn't begin with equal sign. This is equivalent to what happens when setValueExplicit Numeric specifies a non-numeric value.
Added a number of tests from PR #2787.
oleibman