Don't use the bad `FatalError` library.

Only _WIN32 is defined by the compiler, and WIN32 is not standardized
and may be missing.

Closes #169

The initgroups() manpage says we need to check for _BSD_SOURCE.  The
thing is that glibc deprecated this macro, and doesn't define it
anymore, effectively breaking all MPD supplementary groups.

The real fix is to check for initgroups() availability at configure
time, instead of relying on the deprecated _BSD_SOURCE macro.

Haiku does not dump core, it just starts the debugger.

Keep the parent process around until MPD has finished initializing.

This is important for libraries that are allergic to fork(), such as
libupnp.

Prepare for more advanced daemonization code, which will not work with
daemon().  Let's just require fork().  Everybody who supports daemon()
also supports fork().

We can assume that initgroups() would be a no-op in that case, however
initgroups() is not allowed for unprivileged users anyway.

The new class Path only holds a string pointer without being
responsible for allocation/deallocation.  The FileSystem.hxx library
accepts Path arguments instead of AllocatedPath, to avoid forcing
callers to allocate another string object.

Prepare to migrate away from GLib.  Currently, we're still using GLib
as a backend.

Migrate all callers to use Path directly, instead of doing the
conversion in each caller.

These fixes were mostly generated with `codespell' [0] and manually
reviewed.

[0] http://git.profusion.mobi/cgit.cgi/lucas/codespell/

Replaced all occurrences of g_error() with MPD_ERROR() located in a new header
file 'mpd_error.h'. This macro uses g_critical() to print the error message
and then exits gracefully in contrast to g_error() which would internally call
abort() to produce a core dump.

The macro name is distinctive and allows to find all places with dubious error
handling. The long-term goal is to get rid of MPD_ERROR() altogether. To
facilitate the eventual removal of this macro it was added in a new header
file rather than to an existing header file.

This fixes #2995 and #3007.

For systems that cannot support fork() (like no-mmu Linux), use daemon() if
it is available for the daemonizing code.
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

Changed function to first close standard input (this may
fail but we don't care) and then try to open /dev/null (this
may fail but it shouldn't on Unix platforms plus we don't
know what to do in such case anyways).  Since standard input
has the "zeroth" descriptor number next "open" will use it.

Since there is no "/dev/null" on Windows (It's not even
a valid path!) the second step is skipped if WIN32 is
defined.

As a final touch, since the function consists of merely two
function calls it has been moved to header file and declared
static inline.

[mk: un-inline daemonize_close_stdin()]

On Windows only daemonize_close_stdin() function does
something.  Other functions are either empty or generate an
error.  Those have been moved to header file and declared
static inline so compiler can remove the call all together.