implemented native version of FixedTotalNumberConnector
removed assertion line in pyNN.nest.projection._convergent_connect() to enable multapses
Merge branch 'commit_native_fixedtotalnumber_connector' of https://github.com/mschmidt87/PyNN into mschmidt87-commit_native_fixedtotalnumber_connector

Conflicts:
	src/nest/connectors.py
Merge branch 'mschmidt87-commit_native_fixedtotalnumber_connector'