BUG: Including file within a namespace{} is dangerous(unless symbols are within an extern C). Also update documentation about special case for MacOSX

ENH: Adding kwsys implementation for a DynamicLoader class. Copy from itkDynamicLoader, with patch from cmDynamicLoader

ENH: Added kwsys::String class to shorten debugging symbols and error messages involving std::string.

BUG: When more than one command is given and one of them fails to start and the rest are killed, do not forget to reap the killed children.

ENH: Improved robustness of sharing parent pipes with children.  This ensures that the parent pipe handles are inherited by the children.  If a parent pipe handle is invalid a handle to an empty pipe is given to the child to make sure all pipes are defined for the children.