[PATCH] cachemgr migration support

This add a little bit of XHR script to the CGI cachemgr front page which
probes each of the managed proxies for http:// and https:// capabilities
and produces web links to their internal managers.

For the produced links to be usable when viewed from a browser the
http[s]://*/squid-internal-mgr/ URLs should also be updated to produce
an HTML snippet bootstraping a manager viewer such as the javascript one
Kinkie was working on a few months ago. The current situation in 3.2
just links to the plain-text manager menu, which is a bit unfriendly. I
am expecting that we will be able to complete that small update and get
the internal manager a bit more polished before squid-3.3 is released.
So am optimistically targeting the detection in this patch to produce
links for 3.3 and later releases (including 3.HEAD).

This depends loosely on the CORS patch I submitted earlier. Squid which
do not emit the CORS headers are unlikely to pass the XHR scan (a good
thing).

Amos