Merge branch 'ipsec.conf-parser'

Replaces the ipsec.conf parser in starter.  The new parser is also based
on flex/bison but it simply returns key/value collections of all sections.
It already resolves also= and allows overriding options in all included
sections (not only %default), options set in included section can also
be cleared again (key=).  It provides other improvements too, like quoted
strings	(with escape sequences), unlimited includes and better
whitespace/comment handling.

Fixes #423.
Fixes #560.