"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.
Having all functions as static (non-inline) functions generates GCC
warnings, and duplicates binary code across several object files.
Most of dirvec's methods are too complex for becoming inline
functions. Move them all to dirvec.c and publish the prototypes in
dirvec.h.
