rpcd: build, uci and session api fixes

rpcd: build, uci and session api fixes

	- fix CMakeFile to support rpcd out of tree builds
	- fix a possible file descriptor leak in the session deserialization code
	- add uci.state call which is equivalent to uci -P /var/state get ...
	- make uci.changes "config" argument optional to allow listing all deltas in one go
	- fix inverted check in uci.commit and uci.revert, resulting in eroorneous permission denied responses
	- only trigger config change events if libuci was able to parse the config
	- rename misleading "commit" argument of uci.apply to the more appropriate name "rollback"

Signed-off-by: Jo-Philipp Wich <jow@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@39224 3c298f89-4303-0410-b956-a3cf2f4a3e73