Handle Linux/OSX disagreement regarding find options

Linux and OSX (and whatever BSD Apple took their find from) seem to disagree
about the -depth option. All the conditions for a good old fashioned flamewar
are present. Including a passive aggressive comment in the OSX man page about
GNU's misunderstanding of the -d option. org2tex now works on Linux. I tested
on Debian and OSX.

This makes it easier for me to find things to nag you about;)