[LyX/master] Make thin lines exactly 1 pixel wide

[Jean-Marc Lasgouttes]

commit ecd7dee5eab9ac8d57433b2be6912941a807f93b
Author: Jean-Marc Lasgouttes <lasgout...@lyx.org>
Date:   Sat Mar 19 15:48:44 2016 +0100

    Make thin lines exactly 1 pixel wide
    
    The setting of 0 (minimal possible width) was too thin for Mac Retina 
displays.
    
    Fixes bug #10031.

diff --git a/src/frontends/qt4/GuiPainter.cpp b/src/frontends/qt4/GuiPainter.cpp
index 9204c73..b67441b 100644
--- a/src/frontends/qt4/GuiPainter.cpp
+++ b/src/frontends/qt4/GuiPainter.cpp
@@ -46,7 +46,7 @@ using namespace lyx::support;
 namespace lyx {
 namespace frontend {
 
-const int Painter::thin_line = 0;
+const int Painter::thin_line = 1;
 
 GuiPainter::GuiPainter(QPaintDevice * device, double pixel_ratio)
        : QPainter(device), Painter(pixel_ratio),