Used in the generic "CREATE xxx" parsing.
Do some automatic type conversion for inserts from other columns.
Previous trouble with "resjunk" regression test remains for now.
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.