Add ':extend' attribute to faces and themes

Add ':extend' attribute to faces and themes

* etc/themes/wombat-theme.el:
* etc/themes/wheatgrass-theme.el:
* etc/themes/tsdh-light-theme.el:
* etc/themes/tsdh-dark-theme.el:
* etc/themes/tango-theme.el:
* etc/themes/tango-dark-theme.el:
* etc/themes/misterioso-theme.el:
* etc/themes/manoj-dark-theme.el:
* etc/themes/light-blue-theme.el:
* etc/themes/leuven-theme.el:
* etc/themes/dichromacy-theme.el:
* etc/themes/deeper-blue-theme.el:
* etc/themes/adwaita-theme.el: Add ':extend' attribute to all
faces that are by default defined with it.

* lisp/vc/smerge-mode.el (smerge-upper, smerge-lower)
(smerge-base):
* lisp/vc/log-view.el (log-view-file, log-view-message):
* lisp/vc/ediff-init.el (ediff-current-diff-A)
(ediff-current-diff-B, ediff-current-diff-C)
(ediff-current-diff-Ancestor, ediff-even-diff-A)
(ediff-even-diff-B, ediff-even-diff-C)
(ediff-even-diff-Ancestor, ediff-odd-diff-A)
(ediff-odd-diff-B, ediff-odd-diff-C)
(ediff-odd-diff-Ancestor):
* lisp/vc/diff-mode.el (diff-header, diff-file-header)
(diff-removed, diff-added): Make sure all definitions of faces
have the same value of the ':extend' property, otherwise
customizing background color or underline etc. attributes of
these faces on some displays will produce effects different
from other displays.