mergetools: add support for ExamDiff

Signed-off-by: NJacob Nisnevich <jacob.nisnevich@gmail.com>
Acked-by: NDavid Aguilar <davvid@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

mergetools/examdiff

+diff_cmd () {
+	"$merge_tool_path" "$LOCAL" "$REMOTE" -nh
+}
+
+merge_cmd () {
+	touch "$BACKUP"
+	if $base_present
+	then
+		"$merge_tool_path" -merge "$LOCAL" "$BASE" "$REMOTE" -o:"$MERGED" -nh
+	else
+		"$merge_tool_path" -merge "$LOCAL" "$REMOTE" -o:"$MERGED" -nh
+	fi
+	check_unchanged
+}
+
+translate_merge_tool_path() {
+	mergetool_find_win32_cmd "ExamDiff.com" "ExamDiff Pro"
+}