std::stringstream definitely leaks memory (was: Memory leak in ios.cc:326)

[Jerry Quinn]

Benjamin Kosnik writes:
 > 
 > >Did someone open a PR for this?
 > 
 > You just did, thanks.
 > 
 > >It is a very serious bug / regression, not even related
 > >to threads.  ostringstream simply leaks 76 bytes per
 > >creation/destruction.
 > 
 > It's related to the locale cache bits that went in. Jerry, can you take
 > a look at this for the 3.3 branch code? 

OK, I'm starting to look at it now.
Jerry