Patch: name finder fixlets

[Andrew Haley]

Tom Tromey writes:
 > This fixes a couple NameFinder bugs.
 > 
 > First, we fail gracefully if the input stream is closed on us.
 > This can happen if you are running an ancient c++filt.
 > 
 > Second, we don't leak memory, and we allocate less memory in a common
 > case.
 > 
 > Andrew, what do you think?
 > I want to commit to trunk and branch.

Marvellous, thank you.

Andrew.