libsystemd: new library, refactor sd-daemon.[ch] test code

This commit introduces a bare-bones replacement for libsystemd:

 - Build .so file and add --with-libsystemd to configure
 - Add capabilities support to test/src/serv.c
 - Update tests to account for a Finit built w/o libsystemd support

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

libsystemd/sd-daemon.h

@@ -0,0 +1,6 @@
+#ifndef SD_DAEMON_H_
+#define SD_DAEMON_H_
+
+int sd_notify(int unset_environment, const char *state);
+
+#endif	/* SD_DAEMON_H_ */