Adding scoped local set/param declaration to GMPL

[Domingo Alvarez Duarte]

Hello !

I'm experimenting with allow local set/param declarations inside scoped 
blocks (for/if/then/else), it's the base to possibly experiment further 
with problem/callback/function declarations you can see/experiment with 
it in this branch https://github.com/mingodad/GLPK/tree/local-set-param 
, look at 
https://github.com/mingodad/GLPK/blob/local-set-param/examples/shikaku-if.mod 
and 
https://github.com/mingodad/GLPK/blob/local-set-param/examples/test-if.mod 
to see it's usage.

====

for{i in 1..4} {
    printf "now we are at %d\n", i;
    if i mod 2 = 0 then { #assert when missing "= 0"
        param lp := i+10;
        set ls := {1..i+1};
        printf "nested if lp = %d\n", lp;
        display ls;
    }
    param lp := i+20;
    set ls := {1..i+2};
    printf "nested for lp = %d\n", lp;
    display ls;
}

====

Any comment/suggestion is welcome !

Cheers !