Bug #810302

Redevelop auth/saml:
 * remove cludged session handling
 * add sanity checking of ssphp config - must not be phpsession now (use memcache)
 * improve handling of original target URL on login
 * add config option to enable user-login-linking
 * add screen for user to login to local account for linking
 * add linking screen
 * improve error messages

(note: fixed code formatting error found by Jenkins)

Moved login string out to earlier commit

Change-Id: Ib93680e225c325b30b3dc200152590e5e81eaa95
Signed-off-by: Piers Harding <piers@catalyst.net.nz>