Implement default help-echo for mode line.

* lisp/bindings.el: Remove explicit help-echo from format-mode-line.
(mode-line-front-space, mode-line-end-spaces)
(mode-line-misc-info): New variables.
(mode-line-modes, mode-line-position): Move the default value to
the variable definition.
(mode-line-default-help-echo): New defcustom.

* src/buffer.c (buffer_local_value_1): New function, split from
Fbuffer_local_value; can return Qunbound.
(Fbuffer_local_value): Use it.
(Vmode_line_format): Docstring tweaks.

* src/xdisp.c (calc_pixel_width_or_height): Use Fbuffer_local_value.
(note_mode_line_or_margin_highlight): If there is no help echo,
use mode-line-default-help-echo.  Handle the case where the mouse
position is past the end of the mode line string.

* doc/lispref/modes.texi (Mode Line Data): Use "mode line construct"
terminology for consistency.

1 files changed, 12 insertions, 0 deletions

diff --git a/src/ChangeLog b/src/ChangeLog
index b90db0b7fa9..c0098445cb8 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,15 @@
+2012-06-03  Chong Yidong  <cyd@gnu.org>
+
+        * xdisp.c (calc_pixel_width_or_height): Use Fbuffer_local_value.
+        (note_mode_line_or_margin_highlight): If there is no help echo,
+        use mode-line-default-help-echo.  Handle the case where the mouse
+        position is past the end of the mode line string.
+
+        * buffer.c (buffer_local_value_1): New function, split from
+        Fbuffer_local_value; can return Qunbound.
+        (Fbuffer_local_value): Use it.
+        (Vmode_line_format): Docstring tweaks.
+
 2012-06-02  Paul Eggert  <eggert@cs.ucla.edu>
 
         * sysdep.c (system_process_attributes): Improve comment.