patch MAX_NUM_VAR in version 4.0.0

[Bernard M. <me...@it...>]

Dear Madam/Sir,

I always wondered why the number of variables in a user defined function 
is restricted to five. This prevented me from defining "trivial" 
functions such as the scalar product of two vectors in R^3 ...

Changing the line

# define MAX_NUM_VAR    5

in 'syscfg.h' e.g. to:

# define MAX_NUM_VAR   10

and, for consistency, making an appropriate change in 'gnuplot.doc' e.g. to:

New user-defined variables and functions of one through ten variables may
  be declared and used anywhere, including on the `plot` command itself.

  User-defined function syntax:
        <func-name>( <dummy1> {,<dummy2>} ... {,<dummy10>} ) = <expression>

  where <expression> is defined in terms of <dummy1> through <dummy10>.

seems to work OK.

Perhaps the constant MAX_NUM_VAR could in fact be an option in the 
configure/make process?

Anyhow, thank you very much for GNUPLOT!

with best regards,

Bernard Metsch