Summary: A new SSI directive, "ssi.conditional-requests", allows to inform lighttpd which SSI pages should be considered as cacheable and which should not. In particular, the "ETag" & "Last-Modified" headers will only be sent for those SSI pages for which the directive is enabled. Long description: "ETag" and "Last-Modified" headers were being sent for all SSI pages, regardless of whether they were cacheable or not. And yet, there was no cache validation at all for any SSI page. This commit fixes these two minor issues by adding a new directive, "ssi.conditional-requests", which allows to specify which SSI pages are cacheable and which are not, and by adding cache validation to those SSI pages which are cacheable. And since sending ETags for non-cacheable documents is not appropriate, they are no longuer computed nor sent for those SSI pages which are not cacheable. Regarding the "Last-Modified" header for non-cacheable documents, the standards allow to either send the current date and time for that header or to simply skip it. The approach chosen is to not send it for non-cacheable SSI pages. "ETag" and "Last-Modified" headers are therefore only sent for an SSI page if ssi.conditional-requests is enabled for that page. The ssi.conditional-requests directive can be enabled or disabled globally and/or in any context. It is disabled by default. An index.shtml which only includes deterministic SSI commands such as: <!--#echo var="LAST_MODIFIED"--> is a trivial example of a dynamic SSI page that is cacheable.