Let pr_cookie set cookie path for sharing sessions between multiple mounted routers

[davidHMolnar]

Multiple routers could share a session if pr_cookie allows to set an explicit path in the cookie to the common root of all routers, e.g. "/". So having this parameter would be nice.

Currently when multiple routers are mounted, they cannot see each other's cookies and thus sessions. This is because each router sets a cookie whose visibility is restricted to each router's own URI path. Pr_cookie sets no path information with the cookie, and the restriction is the default browser behaviour then.