Turn off TeX for legend labels

[John W. Eaton]

On 15-Apr-2009, Andy Buckle wrote:

| These successfully escape the underscore
|  title("\\_foo")
|  title('\_foo')
|  legend("\\_foo")
|  legend('\_foo')
| 
| These do not
| title('\\_foo')
| legend('\\_foo')

Yes, I think that makes sense given the quoting rules of " vs '
delimeted character strings.

| To summarise
| Bug1: 'interpreter' set to 'none' does not prevent underscores subscripting

This seems to work properly for me in the current development sources,
at least with title objects:

  title ("foo_bar", "interpreter", "none");

| Bug2: some properties of the legend key label text are accessible via
| the plot handles.
| Feature request: make legend key label text properties available somehow.

To be compatible with Matlab, the legend needs to be constructed as a
separate subplot instead of using the "key" feature of gnuplot.

jwe