Allow the bootstrap to be verbose

[mathstuf]

Addresses #264.

[johnbartholomew]

It might be worth noting somewhere that with this patch, configure flags must be separated from bootstrap flags:

This used to work (passing the option through to configure.py):

./bootstrap.py --with-python=/usr/bin/python2

It now fails because the OptionParser in bootstrap.py doesn't recognise the --with-python flag. To avoid this you must use -- to explicitly mark the end of the option flags, like this:

./bootstrap.py -- --with-python=/usr/bin/python2