This commit adds the NeighborPlugin API which can be used to detect
nearby file servers that can be used by input plugins.  This list of
servers is exported using the new "listneighbors" command.  The idle
even "neighbor" notifies interested clients when a new neighbor is
found or an existing one is lost.

There's a lot missing currently: protocol&user documentation, and a
way to "mount" remote servers into the music database.  Obviously,
some code from the UPnP database plugin can be moved to a neighbor
plugin.

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.

Replaces GLib's GError.

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

Better error messages.

Remove the slash hack, allocate memory for the user name.

It's not used anymore, its features have been moved to fd_util.c.

No CamelCase.  Use bool instead of int.  Make both arguments
mandatory.

This updates the copyright header to all be the same, which is
pretty much an update of where to mail request for a copy of the GPL
and the years of the MPD project. This also puts all committers under
'The Music Player Project' umbrella. These entries should go
individually in the AUTHORS file, for consistancy.

Now that I've found this nice function in the GLib docs, we can
finally remove our custom sleep function.  Still all those callers of
g_usleep() have to be migrated one day to use events, instead of
regular polling.

Removed all allocation functions, xwrite(), xread(), ARRAY_SIZE().
Those have been superseded by GLib.

This always allocates strings on the heap, but we can delete the
stripReturnChar() function now.

Currently, both sides of the pipe are blocking, although we do not
need blocking read().  Convert it back to blocking.  Eliminate the
select() from wait_main_task().

Replaced myFgets() with fgets() + g_strchomp().

We want to remove gcc.h eventually. This takes care of all the
G_GNUC_MALLOC macros.

assert_static() will help us to find false asserts in compile time. Of
course it only works in case of expressions which can be evaluated
compile time. It cannot be used in global scope.

Eliminate code already provided by GLib.

"LOG_H" is a macro which is also used by ffmpeg/log.h.  This is
ffmpeg's fault, because short macros should be reserved for
applications, but since it's always a good idea to choose prefixed
macro names, even for applications, we are going to do that in MPD.

Prefer GLib over utils.h.

Remove duplicated code from MPD.

string_toupper() and strDupToUpper() were not able to deal with
character sets other than US-ASCII.  Use GLib's g_utf8_casefold()
for strings.

When there are standardized headers, use these instead of the bloated
os_compat.h.