Implement new conditional USE dep syntax:

Implement new conditional USE dep syntax:

	Conditional evaluation behavior:

		parent state   conditional   result

		 x              x?            x
		-x              x?
		 x             -x?
		-x             -x?           -x

		 x              x=            x
		-x              x=           -x
		 x             x!=           -x
		-x             x!=            x

	Conditional syntax examples:

		compact form         equivalent expanded form

		 foo[bar?]           foo  bar? (  foo[bar] )
		foo[-bar?]           foo !bar? ( foo[-bar] )
		 foo[bar=]           foo  bar? (  foo[bar] ) !bar? ( foo[-bar] )
		 foo[bar!=]          foo  bar? ( foo[-bar] ) !bar? (  foo[bar] )

svn path=/main/trunk/; revision=11231