* ext/tk/lib/tk/canvas.rb: improve coords support for canvas items.
Now, supports all of the followings.
TkcLine.new(c, 0, 0, 100, 100, :fill=>'red')
TkcLine.new(c, [0, 0, 100, 100], :fill=>'red')
TkcLine.new(c, [0, 0], [100, 100], :fill=>'red')
TkcLine.new(c, [[0, 0], [100, 100]], :fill=>'red')
TkcLine.new(c, :coords=>[0, 0, 100, 100], :fill=>'red')
TkcLine.new(c, :coords=>[[0, 0], [100, 100]], :fill=>'red')
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@6309 b2dd03c8-39d4-4d8f-98ff-823fe69b080e