Broken session cookie (w/patch)

The "Redirection cookie (seconds)" field on admin/settings/mobile-tools/device-detection states:

This field is only used when using the ?device= setting. This is the lifetime of the cookie that determines how long the session is remembered. Choose 0 for only the session.

After trying 0, I saw that a immediately expiring cookie, not a session cookie, was being created. That wasn't quite what I was looking for :) After a little tracing, I noticed that the cookie was attempted to be set using a variable called "mobile_tools_cookie_lifetime," defaulting back to some somewhat broken code for $session_time. Not seeing this referenced anywhere else, I'm guessing this was the mistake.

I've refactored $session_time to allow the creation of session cookies, as well as replaced all the mobile_tools_cookie_lifetime references with $session_time. Everything appears to be working as expected!