Only refill captchas when use-captcha? is truthy

Fixes error in tests:

Error: (call-with-input-request) Server error: 500 Internal server error:
  #<URI-common: scheme=http port=8080 host="localhost" path=(/ "paste") query=() fragment=#f>

The error was not showing up because of a bug in server-test (it was
not propagating exceptions).

Signed-off-by: Christian Kellermann <ckeen@pestilenz.org>
Fix I/O redirection when checking for figlet

Signed-off-by: Christian Kellermann <ckeen@pestilenz.org>
Turn figlet-installed? into a procedure

That's to avoid calling figlet when captcha is disabled.

Signed-off-by: Christian Kellermann <ckeen@pestilenz.org>
Add `force-vandusen-notification?' keyword parameter for `pastiche'

Default value: #f.

When set to a truthy value, the "Please notify the #chicken channel on
freenode." checkbox won't be displayed and vandusen will
unconditionally be notified.

This feature is targeted at paste.call-cc.org, which has been used by
spammers from time to time.  Spammers usually uncheck the "notify
vandusen" checkbox, which makes it difficult to track spam pastes.
With this feature, we will at least be notified on #chicken.

Signed-off-by: Christian Kellermann <ckeen@pestilenz.org>
bump version to 0.16