[boost] tweaks for boost::shared_ptr

From: David Abrahams (abrahams_at_[hidden])
Date: 2000-01-03 11:07:22

Conversion from std::auto_ptr<T> to boost::shared_ptr<T> should still
be possible without member templates:

      shared_ptr(std::auto_ptr<T>& r) { 
         pn = new long(1); // may throw
         px = r.release(); // fix: moved here to stop leak if new throws
      } 

A larger question: shouldn't this constructor (and the corresponding
member template) be made _explicit_?