checkIsBoolean: Check if a variable is boolean or not
Description
Checks if a variable is boolean, if not throws an error, otherwise
returns boolean.
Usage
checkIsBoolean(var, name)
Arguments
var
The variable to be checked (if boolean).
name
The name of the variable to appear in any error message.
Value
If not boolean (or NA), throws error.
If NA, return FALSE. Otherwise return
boolean value of var.