config: Added support for specifying include filter patterns.

config: Added support for specifying include filter patterns.

An optional second argument may now be passed to the "Include" configuration
option. If specified (and if the fnmatch() function was available at build
time), only files matching this pattern will be included. For example, the
following will include all files matching "*.conf" in any subdirectory of
/etc/collectd.d/:

  Include "/etc/collectd.d" "*.conf"

This is useful, e.g. for distributions in order to include a possibly empty
directory in the default configuration including all subdirectories but also
making it possible to ship further documents like README files.