Fixing invalid equality comparison between ostreams.

This equality comparison fails on the version of clang++ that comes
with Mavericks, Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM
3.4svn), when compiled with -std=c++0x/c++11.  I'm not sure if it's
*ever* been legal C++ code, but no compiler has complained about it
until now.
Fix signed/unsigned comparison warning in new meshavg code.