interface/connection malloc reductions from mpd-ke

This patch massively reduces the amount of heap allocations at
the interface/command layer.  Most commands with minimal output
should not allocate memory from the heap at all.  Things like
repeatedly polling status, currentsong, and volume changes
should be faster as a result, and more importantly, not a source
of memory fragmentation.

These changes should be safe in that there's no way for a
remote-client to corrupt memory or otherwise do bad stuff to
MPD, but an extra set of eyes to review would be good.  Of
course there's never any warranty :)

No longer do we use FILE * structures in the interface, which means
we don't have to allocate any new memory for most connections.

Now, before you go on about losing the buffering that FILE *
+implies+, remember that myfprintf() never took advantage of
any of the stdio buffering features.

To reduce the diff and make bugs easier to spot in the diff,
I've kept myfprintf in places where we write to files (and not
network interfaces).  Expect myfprintf to go away entirely soon
(we'll use fprintf for writing regular files).

git-svn-id: https://svn.musicpd.org/mpd/trunk@4483 09075e82-0dd4-0310-85a5-a0d7c8717e4f

src/gcc.h

@@ -0,0 +1,50 @@
+#ifndef MPD_GCC_H
+#define MPD_GCC_H
+
+/* this allows us to take advantage of special gcc features while still
+ * allowing other compilers to compile:
+ *
+ * example taken from: http://rlove.org/log/2005102601
+ */
+
+/* disabled (0) until I fix all the warnings :) */
+#if (0 && __GNUC__ >= 3)
+#  define mpd_const		__attribute__ ((const))
+#  define mpd_deprecated	__attribute__ ((deprecated))
+#  define mpd_malloc		__attribute__ ((malloc))
+#  define mpd_must_check	__attribute__ ((warn_unused_result))
+#  define mpd_noreturn		__attribute__ ((noreturn))
+#  define mpd_packed		__attribute__ ((packed))
+/* these are very useful for type checking */
+#  define mpd_printf		__attribute__ ((format(printf,1,2)))
+#  define mpd_fprintf		__attribute__ ((format(printf,2,3)))
+#  define mpd_fprintf_		__attribute__ ((format(printf,3,4)))
+#  define mpd_pure		__attribute__ ((pure))
+#  define mpd_scanf		__attribute__ ((format(scanf,1,2)))
+#  define mpd_unused		__attribute__ ((unused))
+#  define mpd_used		__attribute__ ((used))
+/* #  define inline	inline __attribute__ ((always_inline)) */
+#  define mpd_noinline		__attribute__ ((noinline))
+#  define likely(x)		__builtin_expect (!!(x), 1)
+#  define unlikely(x)		__builtin_expect (!!(x), 0)
+#else
+#  define mpd_const
+#  define mpd_deprecated
+#  define mpd_malloc
+#  define mpd_must_check
+#  define mpd_noreturn
+#  define mpd_packed
+#  define mpd_printf
+#  define mpd_fprintf
+#  define mpd_fprintf_
+#  define mpd_pure
+#  define mpd_scanf
+#  define mpd_unused
+#  define mpd_used
+/* #  define inline */
+#  define mpd_noinline
+#  define likely(x)	(x)
+#  define unlikely(x)	(x)
+#endif
+
+#endif /* MPD_GCC_H */