Covcor converted to cast pipelines + tests

...ibrary/src/com/oracle/truffle/r/library/stats/Covcor.java

...ruffle/r/nodes/builtin/base/foreign/ForeignFunctions.java

...est/src/com/oracle/truffle/r/test/ExpectedTestOutput.test

...cle/truffle/r/test/library/stats/TestExternal_covcor.java