Do not warn when .xts ctor ignores tclass

The current behavior ignores the tclass attribute on the index passed
to .xts(). This is a bug, but throwing a warning breaks existing
packages and causes errors in their CRAN checks. Reinstate the warning
after fixing dependencies.

See #245.

R/xts.R

@@ -166,10 +166,14 @@ function(x=NULL, index, tclass=c("POSIXct","POSIXt"),
     # tclass argument will override the index attribute, but it shouldn't...
     index.class <- attr(index, 'tclass')
     default.class <- c("POSIXct", "POSIXt")
-    if(!is.null(index.class) && !all(index.class %in% default.class)) {
-      warning("the index tclass attribute is ", index.class,
-              " but will be changed to (POSIXct, POSIXt)")
-    }
+### FIXME:
+### This warning causes errors in dependencies (e.g. portfolioBacktest,
+### when the warning is thrown from PerformanceAnalytics). Reinstate this
+### warning after fixing downstream packages.
+###    if(!is.null(index.class) && !all(index.class %in% default.class)) {
+###      warning("the index tclass attribute is ", index.class,
+###              " but will be changed to (POSIXct, POSIXt)")
+###    }
   }
 
   if(hasArg(".indexTZ")) {

inst/unitTests/runit.xts.R

@@ -114,6 +114,7 @@ test..xts_dimnames_in_dots <- function() {
 }
 
 test..xts_ctor_warns_if_index_tclass_not_NULL_or_POSIXct <- function() {
+  DEACTIVATED("Warning causes errors in dependencies")
   op <- options(warn = 2)
   on.exit(options(warn = op$warn))