hg: remove usage of tail+awk in favor of sed

liquidprompt

@@ -847,7 +847,8 @@ _lp_hg_branch_color()
             fi
         else
             local has_lines
-            has_lines=$(hg diff --stat 2>/dev/null | tail -n 1 | awk 'FS=" " {printf("+%s/-%s\n", $4, $6)}')
+            # Parse the last line of the diffstat-style output
+            has_lines="$(hg diff --stat 2>/dev/null | sed -n '$ s!^.*, \([0-9]*\) .*, \([0-9]*\).*$!+\1/-\2!p')"
             if (( commits > 0 )) ; then
                 # Changes to commit and commits to push
                 ret="${LP_COLOR_CHANGES}${branch}${NO_COL}(${LP_COLOR_DIFF}$has_lines${NO_COL},${LP_COLOR_COMMITS}$commits${NO_COL})${has_untracked}${NO_COL}"