replaced jackjack encryption with corrected ecies implementation

This http://en.wikipedia.org/wiki/Integrated_Encryption_Scheme implementation fixes the issues with the current one pointed out by gmaxwell here https://www.mail-archive.com/bitcoin-development@lists.sourceforge.net/msg04311.html

The code is inspired by https://github.com/yann2192/pyelliptic but unlike pyelliptic relies on pure python dependencies https://pypi.python.org/pypi/slowaes/ and https://pypi.python.org/pypi/ecdsa/ instead of OpenSSL.