New strings in gedit

[Ignacio Casal Quinteiro <nacho resa gmail com>]

I added these new strings:

"There was a problem opening the file %s."

"The file you opened has some invalid characters,

if you continue editing this file you could make this

document useless."

"You can also choose another character encoding and try again."

"It is not possible to detect the encoding automatically"

Regards.