Added subset; modified Array's interaction with Function; added new functionality to XdmfInformation subarrays; adjusted documentation to make more uniform

made changes for preparations to push to master; still need to finish documentation changes and line length changes

Eliminate getRealPath calls which are expensive and not necessary in many cases
Parse XML node content only when necessary (parsing arrays)
Fix cases where copies were made of strings instead of using references
Use "map.insert()" rather than "map[] =" when adding properties to map

Using statements have been added to XdmfSharedPtr.hpp. All used of
boost::shared_ptr and boost::shared_dynamic_cast have been replaced
by shared_ptr and shared_dynamic_cast. Slight modification to XdmfCore.i
to get swig wrapping working again.

Added documentation to several methods. Modified Doxygen configuration file to
correctly process macros (tested using Doxygen 1.7.1). Correctly format
documentation to 80 characters per line.

Hopefully this will become a standard style for Xdmf development.
All spaces - 80 character line wrapping.

ENH: Rename all subclasses of XdmfGrid to more syntactically friendly names: i.e. XdmfGridUnstructured to XdmfUnstructuredGrid.

ENH: Added XdmfGridUnstructured and turned XdmfGrid into an abstract base class for all grids (both structured and unstructured).  Modified a bunch of utils and other classes
to fit this new hierarchy.

ENH: Add XdmfGridRegular for CoRectilinear (Regular) Structured Grids.  Add test for interaction and output.