Implement new function `add-face-text-property'

* doc/lispref/text.texi (Changing Properties): Document `add-face-text-property'.

* src/textprop.c (property_set_type): New enum.
(add_properties): Allow appending/prepending text properties.
(add_text_properties_1): Factored out of Fadd_text_properties.
(Fadd_text_properties): Moved all the code into
add_text_properties_1.
(Fadd_face_text_property): New function that calls
add_text_properties_1.

1 files changed, 3 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index d92c9cdec1b..a2ef1c4fdd0 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -103,6 +103,9 @@ Available only on X, this option allows to control over-scrolling
 using the scroll bar (i.e. dragging the thumb down even when the end
 of the buffer is visible).
 
+** New function `add-face-text-property' has been added, which can be
+used to conveniently prepend/append new face attributes to text.
+
 ** In compiled Lisp files, the header no longer includes a timestamp.
 
 ** Multi-monitor support has been added.