Fix a warning in operations on arrays with allocators, stop prohibiting Context+Allocator array construction

Add Enja Tutorial Particles Demo

Fixed an obsolete access to ``obj_ptr`` attribute.

Fallback on file copy on failure to symlink boost.

Fallback on file copy on failure to symlink boost. Fixed install error on Windows 7 with Python 3.3 caused by:
    symlink("boost", bpl_project_boost_inc)
OSError: symbolic link privilege not held

This reverts commit e1a30b51.