This changes no code, makes no moves; this merely adds some headers
to improve readability.

Check for LAME libraries the same way other libraries are checked for, in line
with the configure and outside the buggy macro. This will fix problems with
cross compilation.

This is useful at the maximum depth level, to update newly created
directories.  It is however questionable if the hard-coded 5 seconds
delay is enough to create new directory trees with all of their files,
but we might make that delay configurable in the future.

Limits the depth of the watched directories.  This is useful to keep
resource usage down and speed up MPD startup.