Change Smerge "Mine" and "Other" for "Upper" and "Lower. (Bug#20878)

Change Smerge "Mine" and "Other" for "Upper" and "Lower.  (Bug#20878)

* lisp/vc/smerge-mode.el (smerge-diff-switches)
(smerge-context-menu, smerge-match-conflict, smerge-swap): Doc fixes.
(smerge-upper, smerge-upper-face, smerge-keep-upper)
(smerge-diff-base-upper): Rename from smerge-mine, smerge-mine-face,
smerge-keep-mine, smerge-diff-base-mine.  Update all uses.
(smerge-mine-face, smerge-other-face): Remove obsolete face aliases.
(smerge-lower, smerge-lower-face, smerge-lower-re, smerge-keep-lower)
(smerge-diff-base-lower): Rename from smerge-other, smerge-other-face,
smerge-other-re, smerge-keep-other, smerge-diff-base-lower.
Update all uses.
(smerge-basic-map): Add "l" and "u" bindings.
(smerge-mode-menu): Update menu bindings for renaming.
(smerge-font-lock-keywords): Update face names.
(smerge-match-names): Update names.
(smerge-diff-upper-lower): Rename from smerge-diff-mine-other.
(smerge-match-conflict, smerge-ediff): Rename local variables.
(smerge-makeup-conflict): Relabel markers.
(smerge-parsep-re): Use renamed variables.