Add configuration for cloud.sagemath.com
Add pyzmq package
Add python-readline and tornado
Add IPython yaml
Add IPython to default configuration
Remove implicit dependencies
Merge pull request #12 from certik/smc

Add configuration for cloud.sagemath.com
Add SymPy
Add docutils, pygments and Sphinx
Add the matplotlib package
Build more packages by default
Use bz2 protocol for gmp

The xz protocol does not work on SMC by default (can't import
lzma package).
Build GMP
Remove redundant dependencies

Those are already specified in distutils_package
Simplify Sphinx deps
Use http for GMP download
Remove redundant deps in SymPy
Remove unnecessary deps from pygments
autotools: put -I into CPPFLAGS
Remove redundant lines from png