[TxMt] Re utf-8 encoding and LaTeX Watch + TeXShop

[Robin Houston]

Thanks to Gildas for clarifying the problem off-list.

This appears to be a bug in TeXShop: if you set the default encoding
to UTF-8, and then open a PDF file (not a TeX file) in TeXShop, then
you get this warning message.

I will add a workaround to the next release of Watch, but this should
probably be reported to the developers of TeXShop.

Robin