Not compiling for R 3.1.0

Hi, as I mentioned quantstrat doesn't want to work for 3.1

```
ERROR: dependencies 'quantstrat', 'xtsExtra' are not available for package 'strategery'
* removing 'C:/R/R-3.1.0/library/strategery'
Error: Command failed (1)
In addition: Warning message:
packages ‘quantstrat’, ‘xtsExtra’ are not available (for R version 3.1.0) 
```
