Docs: update doxygen support

[yadij]

Doxygen v1.7.5 changed HTML_HEADER requirements: We now need to add an
open div element to the header that Doxygen then closes for us. This
change also fixes the corresponding generated content on Squid website.

Also, disable IDL_PROPERTY_SUPPORT which has been causing some errors
with output getter/setter matching in the generated output.

[rousskov]

Please share a pointer to the resulting diff exposing changes in Doxygen-generated content.

[rousskov]

Please share a pointer to the resulting diff exposing changes in Doxygen-generated content.

[yadij]

Please share a pointer to the resulting diff exposing changes in Doxygen-generated content.

The first change; to the doxygen.header.dyn file is 7154 chunks identical to the PR diff for doxygen.header.dyn - one for every .dyn produced in the output. These fix the display bug(s) you can see (for now) by visiting http://www.squid-cache.org/Doc/code/ :

• the site menu is rendered outside the main content column area, and
• the navmenu generator scripts abort with an error updating the page DOM. Leaving no tabbed menu for visitors to browse the code docs with.

The second change; to the squid.dox file is a bit subtle. The bug it fixes shows up in some of the images and reference lists for members, only for output produced by recent doxygen versions where the IDL hints are enabled by default.
It can be seen in the doxygen.log error/warnings list as entries like this:

/src/squid/yadij-git/src/auth/basic/Config.cc:70: warning: no uniquely matching class member found for
  const char * Auth::Basic::Config::type() const
Possible candidates:
  'int snmp_mib_tree::type' at line 56 of file /src/squid/yadij-git/include/parse.h
  'u_char variable_list::type' at line 48 of file /src/squid/yadij-git/include/snmp_vars.h
  'int32_t _ntlmhdr::type' at line 82 of file /src/squid/yadij-git/lib/ntlmauth/ntlmauth.h
  'int node::type' at line 109 of file /src/squid/yadij-git/lib/snmplib/parse.c

... where the candidates lists every class where the member name is used by a getter OR setter.

After this PR disabling the hints, doxygen correctly lists more of these candidate lists narrowing it down to only getter or setter. Am not sure why or what is going on - but we are not producing IDL hint files so disabling that unused feature entirely for now.

[kinkie]

ok to test

[yadij]

header regenerated using:

doxygen -w html header.out footer.out style.css squid.dox

A meeting discussion addressed my concern.

[rousskov]

@yadij, I have adjusted PR description to (IMHO) better describe what happened in this PR, but I do not insist on those adjustments. Please feel free to merge with them, without them, or with some further corrections/edits. Thank you.