In systemd v209, released over two years ago, the various libsystemd-*
libraries (libsystemd-journal.so, libsystemd-login.so, libsystem-daemon.so,
libsystemd-id128.so) were merged into a single libsystemd.so library to
reduce code duplication and avoid cyclic dependencies.
Implement BSD/Darwin (kqueue) and Windows (ReadDirectoryChanges) mechanisms
for receiving directory change notifications. Use events instead of polling
for changes. Retry file parsing up to 3 times before giving up.
Huge thanks to missionsix for preparing first two versions of the patch.
Factor out demonization implementation to platform-specific files.
Implement daemonization on Windows using service API. Improve *NIX
implementation by handling signals asynchronously to prevent potential
issues of running complex code inside the handler.
