snapshot.cgi: introduce pause before response

snapshot.cgi: introduce pause before response

Add a pause before responding with snapshot data.  It's only a few
seconds and will not therefore adversely affect any legitimate clients.

However, 'bots and such that cannot afford to spend several seconds
per link are most likely to just give up and go away and cause the
connection to be killed.

To facilitate this, after the pause snapshot.cgi attempts to write
a generic header assuming that if the server has killed the connection
this will cause a SIGPIPE and kill the script.

This shouldn't be necessary to get the script killed early, but is
simply an added feature to assist with the process.

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>