default file suffixes for printing

[Ben Abbott]

I've pushed the changeset below.

        http://hg.savannah.gnu.org/hgweb/octave/rev/944aa97069ed

When an output file is specified but includes no suffix, a proper default is 
inferred from the specified device format.

This is particularly useful for pslatex/epslatex/etc where two files are saved 
(no need to remember if the filename should end with .eps or .tex).

I've also added a check for the specified device when the output is to a 
printer. An error is given if the output is not compatible with a device 
supporting hard copy output.

Ben