Investigate size option versus terminal canvas size option

[zmughal]

In the Gnuplot documentation

$ gnuplot -e 'help size'

it states that the meaning of size used to
be different depending on the terminals. We
should document how to specifically use both
and which version added support for the
terminal canvas size.

[mohawk2]

This is really a Gnuplot matter. Do we need to do anything? Can this be closed?