Upgrade Acl::Node::name to SBuf; remove AclMatchedName global (#1766)

Upgrade Acl::Node::name to SBuf; remove AclMatchedName global (#1766)

AclMatchedName global has been localized into a regular Acl::Answer data
member (Acl::Answer maintains the result of ACLChecklist evaluations).
This long overdue change resolves an old TODO and XXXs, paving the way
for Acl::Node reference counting.

No significant functionality changes are expected, but it is possible
that some deny_info configurations will now be handled better in
reconfiguration corner cases (because Squid no longer forgets the name
of the last checked ACL when a slow ACL check crosses reconfiguration
barrier).

Most of these changes are performance-neutral or -positive because they
eliminate or reduce memory allocations and associated name copying (and
more reduction will become possible after upgrading squid.conf parsers
to use SBuf). This change adds SBuf object copies when Acl::Answer is
propagated to ACLCB callbacks, but those read-only copies are cheap.

Also renamed and polished aclGetDenyInfoPage() because we had to update
its parameter type (to supply the last evaluated ACL). All callers were
also supplying the same first argument (that is unlikely to change in
the foreseeable future); that argument is now gone. We  did not fix the
redirect_allowed name and debugs(): Fixing that behavior deserves a
dedicated change.

Also polished legacy aclIsProxyAuth() profile and description because we
have to change the parameter type (to supply the last evaluated ACL).

Also removed 63-character aclname parameter limit for acl directives.