Login flow redirects to landing page instead of previous page

[bmispelon]

I noticed today that the login process seems to lose track of where the user is coming from:

• Visit a ticket page while not logged in
• Click "Login" in the navigation
• Choose "log in with github"

Once login is successful, I find myself redirected to the root page / and not the ticket page that I was browsing when I clicked the "Login" link.

It's slightly annoying and I think it should be fixable by passing the right redirection URL to the login page (via a GET parameter).

[bmispelon]

As reported in #204, this bug ends up breaking the RSS links on the timeline and query pages.

I took a brief look at the problem a few weeks back, and from what I can tell the issue is that the plugin we use for github auth (https://github.com/trac-hacks/trac-github/) doesn't seem to support passing a redirection parameter to control where the user ends up after a successful login.