[dw-free] Update direct referer checks to use check_referer instead

[kareila]

[commit: http://hg.dwscoalition.org/dw-free/rev/48a8800d5eec]

http://bugs.dwscoalition.org/show_bug.cgi?id=1557

Replace regexp referer checks with the check_referer function.

Patch by draigwen.

Files modified:

• htdocs/interests.bml
• htdocs/login.bml
• htdocs/logout.bml

( Diff: 3 files changed. )