Make crypto backend configurable.

With this commit, no actively used code outside sigver.py really
knows about xmlsec1.
Remove unused module.

Roland believes this module can be removed - leftovers from some
earlier refactoring.
Avoid hard xmlsec_binary requirement for ECP client.

By providing an already initialized Config() instance, an ECP
client using another CryptoBackend than xmlsec1 can be instantiated.
Remove obsolete xmlsec_path from pathutils.
Merge branch 'master' of https://github.com/rohe/pysaml2

Conflicts:
	src/saml2/config.py
	tests/idp_conf.py
	tests/servera_conf.py
Support configurable crypto backends.
Merge pull request #34 from fredrikt/master

Make crypto backend configurable.