Currently force the type to match the _first_ select in the union.
Move oper_select_candidate() from parse_func.c to parse_oper.c.
Throw error inside of oper_inexact() if no match for binary operators.
Check more carefully that types can be coerced
even if there is only one candidate operator in oper_inexact().
Fix up error messages for more uniform look.
Remove unused code.
Fix up comments.
varchar length.
Cleans up code so attlen is always length.
Removed varchar() hack added earlier.
Will fix bug in selecting varchar() fields, and varchar() can be
variable length.