Add a Frozen class to restrict creation of new fields in Python classes
Log: Make cache_initial_output a nop if log_file already exists
tryfile: Add pack/unpack support replacing files with strings
PolygonMesh.h: Fix indentation
Value.h: Remove spaces before semicolons
value/Worker: Add a facility for asynchronous value computation on separate processes
solver/brent.cpp: clang found a scoping bug

I introduced a bug when I ported brent over from scipy.
SConstruct: Minor changes for BlueGene

1. Use -std=c++11 instead of -std=c++0x.
2. Don't use -dead_strip with clang.
3. Make powerpc optimization flags the same as native's.
SConstruct: Make it easy to adjust optimization flags