Issue #18278: properly document how the loaders are called for FileFinder
BSD: block devices are gone
http://www.freebsd.org/doc/en/books/arch-handbook/driverbasics-block.html
#18113: avoid segfault if Py_XDECREF triggers code that calls set_panel_userptr again

Problem noted & original patch by Serhiy Storchaka; I tweaked the patch a bit.