Extend list of x aesthetics

So that they are symmetric with y aesthetics.
Needed for ggstance.

Author: lionel-

NEWS.md

@@ -1,3 +1,9 @@
+# ggplot2 2.1.0.9000
+
+* `x` and `y` scales are now symmetric regarding the list of
+  aesthetics they accept: `xmin_final`, `xmax_final`, `xlower`,
+  `xmiddle` and `xupper` are now valid `x` aesthetics.
+
 # ggplot2 2.1.0
 
 ## New features

R/scale-continuous.r

@@ -82,7 +82,7 @@ scale_x_continuous <- function(name = waiver(), breaks = waiver(),
                                limits = NULL, expand = waiver(), oob = censor,
                                na.value = NA_real_, trans = "identity") {
   sc <- continuous_scale(
-    c("x", "xmin", "xmax", "xend", "xintercept"),
+    c("x", "xmin", "xmax", "xend", "xintercept", "xmin_final", "xmax_final", "xlower", "xmiddle", "xupper"),
     "position_c", identity, name = name, breaks = breaks,
     minor_breaks = minor_breaks, labels = labels, limits = limits,
     expand = expand, oob = oob, na.value = na.value, trans = trans,