Fix regression in account merge w/ Aspen upgrade

We do an internal redirect as part of account merge, and we didn't
update the filename of confirm.html.spt when we upgraded to Aspen 0.25
(#888).
Fix bug in account merge (#1226)

Bountysource uses 'display_name' but we, under the influence of Twitter,
were trying to access 'screen_name'. This only shows up if there is a
bountysource account in the mix when merging accounts.
Merge branch 'master' into fix-account-merge
Merge pull request #1225 from gittip/fix-account-merge

Fix regression in account merge w/ Aspen upgrade