Merge pull request #318 from joegallo/master

Compilation errors with boost 1.56
Revert "fix "type 'char' cannot be used prior to '::'""

This reverts commit 38557ee63273dcdef22b136c5f424802c7ff6e03.
Revert "fix "no viable conversion from ... to 'bool'""

This reverts commit df9ae3ab9b37fde803f26c6bc4eaadfd67fc1d07.
use explicit NULL comparisons

fixes a compilation error with boost 1.56
#if guard for boost 1.56 compatibility