Workaround OSX clang broken map operator[] using ifdef guards and manual find/insert.
Merge pull request #81 from danielhams/clangworkarounds

Clang workarounds for broken map operator[]
Merge branch 'develop' into dhdevelop
Switch back to normal map for the moment.
Implement optimised hash and equality operators for h256, and specialise std::hash<eth::h256>.
Hash instructions require at least one on stack.
Merge branch 'develop' of github.com:ethereum/cpp-ethereum into develop
Fixed hash so compiles in a C++ compiler. Not sure what compiler Tim was
using.
Merge branch 'develop' into dhdevelop