destroyable.h

[mrkraimer]

Currently code often has to implement an empty destroy method.
I think that if

virtual void destroy() = 0;

is replaced with

virtual void destroy() {}

then other code does not have to implement an empty destroy method

[mrkraimer]

Now that a new release of EPICS7 is available, can Michael now make this change?

[mdavidsaver]

Done. 598fa1e