[OS X Emacs] sync with Skim

[Jan Rosinski]

I have noticed that if I use preview in line in latex mode,
update a formula and regenerate its preview (at point),
then Skim does not update the pdf, no matter how many
typesettings I run.
I have to close Skim's preview file and generate a new one.
I have observed this annoying behavior syncing with the newest Skim  
1.2.1,
I do not know whether it was present in earlier versions.

Jan