migration to DirectorOpener / Sso bypass related code

[jkbzh]

Rewrite of http_auth.py module to use OpenerDirector handlers, fix some sec issues
and add bypass header functionality

replaced deprecated FancyURLOpener with OpenerDirector handlers.
security issue: url safety checks were only done against the first
opened url, but not against others if that first url was redirected
elsewhere
new option to add a configurable bypass header
removed basic auth code as we were not using it
merged class ProxyAuthURLopener into ProtectedURLopener as there
was no contemporary reason why they should be separated.
ProxyAuthURLopener is still available, but it's a dummy class that
acts as an alias for ProtectedURLopener, to be deprecated when
we finish updating scripts that use this class.
added testsuite to ease updating of the code