cache/cluster session backend fixes

Important fixes to the cache/cluster session, for bugs introduced in 3.0.15.

SSL changed to use blocking read/write

The SSL and JNI sockets now use blocking reads and writes.

host/web-app merging

<host> merging now uses the <host-name> values.

cache-mapping additions

The <cache-mapping> tag now allows url-regexp.

<max-age> replaces <expires>.

<s-max-age> added.