Matplotlib: make it discover pkg-config files

Fixes #45. This has been fixed in hashstack1, the issue is that the only way to
force Matplotlib to use our png and our freetype (as opposed to systewide) is
by using pkg-config. So we just need to let it know where the .pc files are.
Add and use libflags
Add FFTW package
Add netcdf4 Fortran library
Add FFTW 2 package

This is only useful for backwards compatibility, thus we name it fftw2. In all
packages, you should just use FFTW 3 (the fftw package), unless you really need
FFTW 2.
updated libpng url to what we hope is a permanent one
Merge pull request #48 from certik/mpl2

Mpl fix rpath
Merge pull request #49 from certik/fftw

Add FFTW package
Merge pull request #50 from certik/netcdf4f

Add netcdf4 Fortran library
Add fabric, fabric-virtualenv, paramiko, pycrypto

paramiko is a dependency to fabric and pycrypto
is a dependency to paramiko.
Add Fabric to a test
Merge pull request #51 from certik/fabric

Add fabric, fabric-virtualenv, paramiko, pycrypto
Add ncurses, openssl, readline and sqlite
Test the newly added packages
Merge pull request #52 from certik/python_prerequisites

Python prerequisites
Implement Python standard library module tests

This commit adds:

* all optional dependencies of Python
* test that all standard library modules actually install and work
Fix petsc to build again on Linux
Python: make bzip2 and openssl deps optional

Only use them on linux. Update tests to include bzip2 and openssl explicitly.
Fix the test.host-scipy.yaml test

We need to specify the 'build_with' option to Python.
Remove 'python-readline' dep. from ipython

The readline module is now build into Python itself, so this extra module is
not necessary anymore.