[glib] tests: Add some documentation to the illegal sequence conversion test

[Philip Withnall <pwithnall src gnome org>]

commit 3a88ab6c257558406cbc0caab25bb941764ca156
Author: Philip Withnall <withnall endlessm com>
Date:   Mon Jan 22 12:54:51 2018 +0000

    tests: Add some documentation to the illegal sequence conversion test
    
    Signed-off-by: Philip Withnall <withnall endlessm com>
    
    https://bugzilla.gnome.org/show_bug.cgi?id=790698

 glib/tests/convert.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/glib/tests/convert.c b/glib/tests/convert.c
index 4229897..03c0d72 100644
--- a/glib/tests/convert.c
+++ b/glib/tests/convert.c
@@ -54,7 +54,9 @@ test_iconv_state (void)
   g_free (out);
 }
 
-/* some tests involving "vulgar fraction one half" */
+/* Some tests involving "vulgar fraction one half" (U+00BD). This is
+ * represented in UTF-8 as \xC2\xBD, in ISO-8859-1 as \xBD, and is not
+ * represented in ISO-8859-15. */
 static void 
 test_one_half (void)
 {