libid3tag comes without a pkg-config file, and it is usually added by
distribution packages.  For those without .pc file, attempt to
auto-detect the library with AC_CHECK_LIB.

When the decoder of the new song is not fast enough, the player thread
has to wait for it for a moment.  However the variable "nextChunk" was
reset to -1 during that, making the next loop iteration assume that
cross-fading has not begun yet.  This patch overwrites it with "0"
while waiting.

The icy_metadata will be used by the curl input_stream implementation.

The tag() method reads a tag from the stream.  This replaces the
meta_name and meta_title attributes.

tag_merges() merges the data from two tag objects into one.

This patch fixes a minor memory leak: when decoder_tag() attempted to
send a merged tag object (created by tag_add_stream_tags()), and was
interrupted by a decoder command, it did not free the temporary merged
tag object.

Don't use g_strescape(), because it escapes all non-ASCII characters.
Add a new function which clears all non-printable characters, not just
"newline".

Commit b3e2635a introduced a regression: when a stream tag was
changed, the playlist version had to be updated.  This was done in
syncCurrentPlayerDecodeMetadata(), called by syncPlayerAndPlaylist().
After b3e2635a, this was not called anymore.  Fix this by emitting
PIPE_EVENT_PLAYLIST.

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Those have been superseded by GLib.

xclose() aims to be the signal safe version of close(). However during
cleanup, this isn't important.

If the state file cannot be read, for whatever reason, don't abort
MPD.  The state file isn't _that_ important.

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

Don't use libc's rand() function, because it is slow.  Our own trivial
linear congruential generator is good enough for dithering.

The length of GREETING is known at compile time, don't use strlen().

WIN32 has no getaddrinfo().  Fall back to gethostbyname().

Windows has no pipe(), it only has _pipe() with two additional
parameters.

All socket functions are provided by ws2_32.dll.

g_strsplit() is more portable than strtok_r().

g_strsplit() is more portable than strtok_r().

Use strchr()/g_strndup() to extract the password.