pipe: pipe base class needs a virtual destructor
pipe: pipe base class needs a virtual destructor

Since pipe is meant to be subclassed (and has to be, since it's
abstract), it needs a virtual destructor.  Otherwise the subclass
destructor may not get called.  Yay C++.

aclements/sv6,aclements/sv6,aclements/sv6,bowlofstew/sv6,bowlofstew/sv6,bowlofstew/sv6,aclements/sv6,bowlofstew/sv6,aclements/sv6,bowlofstew/sv6