Compressed io fix

[sshiraiwa]

This pull will addresses the following issues

• GridFunction(std::istream &) is called, it did not return a proper object when the argument is IOString.
• When the filename is passed it is interpreted as a filename. When the file is compressed it does not detect it automatically.
• Some routines generated using &feature("shadow") did not work in subclasses
• STRUMPACK_DIR was not passed properly to CMake in setup.py

It also adds

• PrintGZ (and similar methods) to GridFunction, Mesh, and other classes which generate a compressed file.

#81
#80