Use memmove() rather than memcpy() in set_var_from_var(). If this function

Use memmove() rather than memcpy() in set_var_from_var(). If this function
is asked to assign a variable to itself, it will result in doing a
memcpy() on an entirely-overlapping memory range, which results in
undefined behavior according to ANSI C. That said, it is unlikely to
actually do anything bad on any sane libc, but this keeps valgrind quiet.