Add an optional testfn parameter to assoc

* src/fns.c (assoc): New optional testfn parameter used for comparison
when provided.
* test/src/fns-tests.el (test-assoc-testfn): Add tests for the new
'testfn' parameter.
* src/buffer.c:
* src/coding.c:
* src/dbusbind.c:
* src/font.c:
* src/fontset.c:
* src/gfilenotify.c:
* src/image.c:
* src/keymap.c:
* src/process.c:
* src/w32fns.c:
* src/w32font.c:
* src/w32notify.c:
* src/w32term.c:
* src/xdisp.c:
* src/xfont.c: Add a third argument to Fassoc calls.
* etc/NEWS:
* doc/lispref/lists.texi: Document the new 'testfn' parameter.

1 files changed, 5 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index a00760c2f8e..68ebdb3c15c 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -100,6 +100,11 @@ required capabilities are found in terminfo.  See the FAQ node
 
 * Changes in Emacs 26.1
 
++++
+** The function 'assoc' now takes an optional third argument 'testfn'.
+This argument, when non-nil, is used for comparison instead of
+'equal'.
+
 ** The variable 'emacs-version' no longer includes the build number.
 This is now stored separately in a new variable, 'emacs-build-number'.