load-fragment: properly unescape \;

https://bugs.freedesktop.org/show_bug.cgi?id=87393
test-unit-file: add test for semicolon escaping

https://bugs.freedesktop.org/show_bug.cgi?id=87393
core: use raw_clone instead of fork in signal handler

fork() is not async-signal-safe and calling it from the signal handler
could result in a deadlock when at_fork() handlers are called. Using
the raw clone() syscall sidesteps that problem.

The tricky part is that raise() does not work, since getpid() does not
work. Add raw_getpid() to get the real pid, and use kill() instead of
raise().

https://bugs.freedesktop.org/show_bug.cgi?id=86604