Remove miter-precision from XFAIL

The miter-precision PS output prints correctly on my LaserJet 4050. So
file a Ghostscript bug, supply PS ref images and remove from XFAIL.

test/Makefile.am

@@ -909,7 +909,6 @@ extend-pad$(EXEEXT)				\
 filter-nearest-offset$(EXEEXT)			\
 filter-bilinear-extents$(EXEEXT)		\
 long-lines$(EXEEXT)				\
-miter-precision$(EXEEXT)			\
 operator$(EXEEXT)				\
 operator-alpha$(EXEEXT)				\
 self-copy-overlap$(EXEEXT)			\

test/README

@@ -261,3 +261,8 @@ Incorrect clipping of group object (regression?)
 https://bugs.freedesktop.org/show_bug.cgi?id=14580
 --------------------------------------------------
 push-group
+
+Ghostscript does not correctly render small miters
+http://bugs.ghostscript.com/show_bug.cgi?id=690098
+--------------------------------------------------
+miter-precision

test/miter-precision.c

@@ -38,7 +38,7 @@ static cairo_test_draw_function_t draw;
 static const cairo_test_t test = {
     "miter-precision",
     "test how cairo deals with small miters"
-    "\nPS backend currently fails for unknown reason (cairo? GS?).",
+    "\nPS backend currently fails due to GS bug.",
     120, 100,
     draw
 };