Handle 'x' and 'xout' args in na.locf.xts()

The na.locf.xts() method did not support 'x' and 'xout', like the
default method does. The easiest way to support these arguments is to
check if they're part of the call, then punt to the next method if
they are.

Fixes #215.

R/na.R

@@ -97,6 +97,8 @@ na.locf.xts <- function(object, na.rm=FALSE, fromLast=FALSE, maxgap=Inf, ...) {
     maxgap <- min(maxgap, NROW(object))
     if(length(object) == 0)
       return(object)
+    if(hasArg("x") || hasArg("xout"))
+      return(NextMethod())
     if(dim(object)[2] > 1) {
       x <- object
       for(n in 1:NCOL(object))

inst/unitTests/runit.na.locf.R

@@ -34,3 +34,18 @@ test.nalocf_fromLast <- function() {
   z <- na.locf(zdat, fromLast = TRUE)
   checkEquals(x, as.xts(z), check.attributes = TRUE)
 }
+
+test.nalocf_x <- function() {
+  xidx <- rbind(xidx, .xts(0, 30))
+  zidx <- as.zoo(xidx)
+
+  x <- na.locf(xdat, x = index(xidx))
+  z <- na.locf(zdat, x = index(zidx))
+  checkEquals(x, as.xts(z), check.attributes = TRUE)
+}
+
+test.nalocf_xout <- function() {
+  x <- na.locf(xdat, xout = index(xidx))
+  z <- na.locf(zdat, xout = index(zidx))
+  checkEquals(x, as.xts(z), check.attributes = TRUE)
+}