This fix partially #2142

(and add ftp and smb to the list)

Basically this test was expecting that /tmp is a directory. On Mac OS X /tmp is a link to /private/tmp.

We work around by getting the current work directory after chdir.

 It fixed a segfault when using hotkeys for the OSD.
 I am not sure it is perfectly fine, but var_AcquireMutex seems
to have been removed without a proper replacement.

Should we keep this code?

This should fix the compilation of pda interface.

We want the current playing item, rather than the number of items to
choose from. Besides, item-current is _not_ a choice list anyway.

None of the callers actually care about the return value anyway.
When the input item is needed, then playlist_AddInput did and still
does the job.