Validate case statements for case variables
ensureValidCase(case)a list for one case to test
List elements:
id: an integer to use for this category when a case variable is made
(default: none, one will automatically be assigned when the case variable
is made)
name: a character identifier for this case
expression: a CrunchLogicalExpr that sets the conditions for the case, or "else"
numeric_value: a numeric that is the value this case should take on
when analyzing the data numerically (mean, standard deviation, etc.)
missing a logical indicating if this case should be treated as missing