Minor emerge changes.

Minor emerge changes.
* lisp/vc/emerge.el (emerge-eval-in-buffer): Remove, and replace all uses
with with-current-buffer.
(diff, template): Give dynamic local variables a prefix.
(emerge-line-numbers): Rename local `diff' to emerge-line-diff.
(emerge-line-number-in-buf): Update for above name change.
(emerge-combine-versions-internal): Rename local `template' to
emerge-combine-template.
(emerge-combine-versions-edit): Update for above name change.