… install-time.

Users may install from pip or easy_install without having PySide or PyQt4 installed.
However if they want to build from a mercurial clone alone, they will need to
have PySide and pyside-rcc, and/or PyQt4 and pyrcc4, whicher they want to use
support for either can be enabled and disabled via boolean flags at the top
of setup.py.

Bumped version to 1.4.0