[Rd] biplot(mva): argument main causes a warning

[Wolfram Fischer - Z/I/M]

PROBLEM
	If `main' is given as argument to biplot() a warning appears:
	parameter "main" couldn't be set in high-level plot() function

PROPOSAL FOR A SOLUTION
	biplot.default( ....., main=NULL, ...){
		...
		plot( ......, main=main, ... )
		...
		plot( ......, main=main, ... )
		...
	}
	
Wolfram