[mod_userdir] add userdir.active option, "enabled" by default

git-svn-id: svn://svn.lighttpd.net/lighttpd/branches/lighttpd-1.4.x@2880 152afb58-edef-0310-8abb-c4023f1b3aa9
[mod_user] add test cases to check handling of encoded ~ as %7E (#2124)

git-svn-id: svn://svn.lighttpd.net/lighttpd/branches/lighttpd-1.4.x@2881 152afb58-edef-0310-8abb-c4023f1b3aa9