Use fl_xyline() and fl_yxline() that are better for horizontal and vertical lines.

git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10460 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Remove unnecessary statement.

git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10461 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Matches CGContextSaveGState() with corresponding CGContextRestoreGState().

git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10462 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Added full support of retina displays on the mac platform.
On such displays, one drawing unit equals two pixels.
The fl_xyline() and fl_yxline() functions are modified to perform
extra operations when drawing to a window on a retina display.

git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10463 ea41ed52-d2ee-0310-a9c1-e6b18d33e121
Carbon function TSMGetActiveDocument() and its friends are no longer documented on the Apple web site.
Don’t use them unless Fl::disable_im() is called.

git-svn-id: http://seriss.com/public/fltk/fltk/branches/branch-1.3@10464 ea41ed52-d2ee-0310-a9c1-e6b18d33e121