build: fix out of src tree builds

Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
build: add ability to disable sendfile checks

Add the ability to disable checking for sendfile support.

Even though the target may have the support we may not want to use it, this
is true in the case of broken terastation support.

Default is to check for sendfile support, so no change in behaviour.

Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
upnpsoap: remove 384 char description limit

The description limit is currently hardcoded. This is fine until the limit
is reached and the resp string does not get terminated correctly.

This causes issues and usually ends with the client silently closing the
connection.

Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
scanner: enable optional scan of hidden directories

Mainly used for testing.

Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
build: add include for missing PATH_MAX

May well be a broken toolchain, however this enables us to build on a
powerpc based terastation running 2.3.2 glibc - very old.

Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
albumart: search for .tbn rather than .jpg album art

The is really only to be compliant with a shared xbmc and minidlna
directory.

Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>