Remove a useless creation of a BaseString object with a C string in
comparison operators of this class, because there is a function
equals() that accepts a C string in parameter.
The call to decRefCount has been moved to the destructor
of the base class BaseString.
Note that BaseString only exists for the purpose of being able
to reuse code for our String and U32String implementations. As
such it is not meant to be used polymorphically and its
destructor does not need to be virtual (with the overhead that
this generates). And to ensure that it is not used in a
polymorphic way, the destructor is declared protected.
Appending \0 to string and expecting it to be just dropped is
still an invalid behaviour but it already happened in 2 engines, so
restore old behaviour, at least for now
