Add a method that checks a symbol for structural validity
according to some predetermined rule, and add it as an
extra rule for symbol-table validity that each symbol is
well-formed.
result2 was never used, although it was meant to be tested for. Renamed it to
result_add_2 (and result_add_1) instead to make it clearer and more obvious.
This wraps a symbol table, providing an interface matching its write side
(but not type-compatible, to avoid implicit casts between the two), and
journals modifcations such that callers can determine what changes were made
by code using this wrapper to add, update and remove symbols
Michael Tautschnig