Separate border width for floating windows

Floating windows already had their own border style, but the width was
the same for all windows.

The configuration directives 'new_window' and 'new_float' can now be
used simultaneously to have different border widths for floating and
tiled windows.

fixes #1244

src/config.c

@@ -255,6 +255,7 @@ void load_configuration(xcb_connection_t *conn, const char *override_configpath,
     config.default_border = BS_NORMAL;
     config.default_floating_border = BS_NORMAL;
     config.default_border_width = logical_px(2);
+    config.default_floating_border_width = logical_px(2);
     /* Set default_orientation to NO_ORIENTATION for auto orientation. */
     config.default_orientation = NO_ORIENTATION;