Change default mark advance zeroing behavior from Unicode to GDEF

See thread at:
https://lists.freedesktop.org/archives/harfbuzz/2016-February/005462.html

src/hb-ot-shape-complex-default.cc

diff --git a/src/hb-ot-shape-complex-default.cc b/src/hb-ot-shape-complex-default.cc
index 5cf0a18..be60e56 100644
--- a/src/hb-ot-shape-complex-default.cc
+++ b/src/hb-ot-shape-complex-default.cc
@@ -40,6 +40,6 @@
   NULL, /* decompose */
   NULL, /* compose */
   NULL, /* setup_masks */
-  HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_UNICODE_LATE,
+  HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
   true, /* fallback_position */
 };

src/hb-ot-shape-complex-thai.cc

diff --git a/src/hb-ot-shape-complex-thai.cc b/src/hb-ot-shape-complex-thai.cc
index bd7c5e1..58392b6 100644
--- a/src/hb-ot-shape-complex-thai.cc
+++ b/src/hb-ot-shape-complex-thai.cc
@@ -377,6 +377,6 @@
   NULL, /* decompose */
   NULL, /* compose */
   NULL, /* setup_masks */
-  HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_UNICODE_LATE,
+  HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
   false,/* fallback_position */
 };

src/hb-ot-shape-complex-tibetan.cc

diff --git a/src/hb-ot-shape-complex-tibetan.cc b/src/hb-ot-shape-complex-tibetan.cc
index 03bcfee..a77b531 100644
--- a/src/hb-ot-shape-complex-tibetan.cc
+++ b/src/hb-ot-shape-complex-tibetan.cc
@@ -57,6 +57,6 @@
   NULL, /* decompose */
   NULL, /* compose */
   NULL, /* setup_masks */
-  HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_UNICODE_LATE,
+  HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
   true, /* fallback_position */
 };