finish BOOLEAN()

[GillesDuvert]

BOOLEAN() is just a .pro at the moment.
To enable correct support boolean should be a C++ variant of DByteGDL ansd proper actions be taken at various places.

a = [0.0, 1.0, 0.0, 3.0]
b = BOOLEAN(a) ; --> works: b=[0,1,0,1]
c = boolean("no") ; -->works: c=1 ; not 0 as you may think --- booleans are not really that smart. 
b[2] = "yes" ; equal to "true"
HELP, b ; does not work: should be [0,1,1,1] , GDL gives [0,1,121,1]