Use the same diff color scheme as in modern VCSes (bug#10181).

Use the same diff color scheme as in modern VCSes (bug#10181).

* lisp/vc/diff-mode.el (diff-header, diff-file-header): Remove "green"
to avoid confusion with `diff-added' that now uses green colors.
(diff-removed): Use shades of red.
(diff-added): Use shades of green.
(diff-changed): Leave just the yellow color.
(diff-use-changed-face): New variable.
(diff-font-lock-keywords): Use `diff-use-changed-face' to decide
how to highlight context diff changes.
(diff-refine-change): Use shades of yellow.
(diff-refine-removed): New face that uses shades of red.
(diff-refine-added): New face that uses shades of green.
(diff-refine-hunk): Use `diff-refine-change', `diff-refine-added',
`diff-refine-removed' in the call to `smerge-refine-subst'
depending on the value of `diff-use-changed-face'.

* lisp/vc/ediff-init.el (ediff-current-diff-A, ediff-fine-diff-A):
Add face condition `min-colors 88' with shades of red.
(ediff-current-diff-B, ediff-fine-diff-B): Add face condition
`min-colors 88' with shades of green.
(ediff-current-diff-C, ediff-fine-diff-C): Add face condition
`min-colors 88' with shades of yellow.

* lisp/vc/smerge-mode.el (smerge-mine): Use shades of red.
(smerge-other): Use shades of green.
(smerge-base): Use shades of yellow.
(smerge-refined-change): Empty face.
(smerge-refined-removed): New face that uses shades of red.
(smerge-refined-added): New face that uses shades of green.
(smerge-refine-subst): Rename arg `props' to `props-c'.  Add new
args `props-r' and `props-a', and use them.  Doc fix.
(smerge-refine): Evaluate `smerge-use-changed-face' and depending
on its value use different faces `smerge-refined-change',
`smerge-refined-removed', `smerge-refined-added' in the call to
`smerge-refine-subst'.