Don't show pylab's welcome message when creating a new session

Previously:

$ bin/isympy -q

Welcome to pylab, a matplotlib-based Python environment [backend: agg].
For more information, type 'help(pylab)'.
IPython console for SymPy 0.7.3-git (Python 2.7.2-64-bit) (ground types:
gmpy)

In [1]:

Now:

$ bin/isympy -q
IPython console for SymPy 0.7.3-git (Python 2.7.2-64-bit) (ground types:
gmpy)

In [1]: