uhttpd: do not attempt to configure Lua handler if referenced file does not exist

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@40457 3c298f89-4303-0410-b956-a3cf2f4a3e73
uci: fix import with not yet existing packages, preserve config permissions on commit, fix Lua detection in cmake

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@40458 3c298f89-4303-0410-b956-a3cf2f4a3e73