[API] Add hb_language_get_default()
It uses locale information to detect default language. It's used by
hb_shape() whenever language is not set on the buffer.
Not sure how to properly test it in the test suite. Tested by observing
that with DejaVu Sans we select the proper local glyph version for U+431
under Serbian locale. See http://www.pango.org/ScriptGallery
diff --git a/src/hb-common.h b/src/hb-common.h
index 64109da..9546b21 100644
--- a/src/hb-common.h
+++ b/src/hb-common.h
@@ -113,6 +113,9 @@
const char *
hb_language_to_string (hb_language_t language);
+hb_language_t
+hb_language_get_default (void);
+
/* hb_unicode_general_category_t */
