[mod_userdir] use 2-element cache
[mod_userdir] use 2-element cache

use 2-element cache, can be getpwnam() lookup is expensive

cache lifetime is 60 seconds
homedir paths are not expected to change quickly

gstrauss/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4