implement warn option on readLines

...cle/truffle/r/nodes/builtin/base/ConnectionFunctions.java

...in/src/com/oracle/truffle/r/nodes/builtin/base/Parse.java

.../src/com/oracle/truffle/r/nodes/builtin/base/ReadDCF.java

...tin/src/com/oracle/truffle/r/nodes/builtin/base/Scan.java

...e/truffle/r/nodes/builtin/base/foreign/ReadTableHead.java

.../com/oracle/truffle/r/runtime/conn/ConnectionSupport.java

...rc/com/oracle/truffle/r/runtime/conn/FileConnections.java

...rc/com/oracle/truffle/r/runtime/conn/GZIPConnections.java

...me/src/com/oracle/truffle/r/runtime/conn/RConnection.java

.../com/oracle/truffle/r/runtime/conn/SocketConnections.java

...src/com/oracle/truffle/r/runtime/conn/StdConnections.java

...rc/com/oracle/truffle/r/runtime/conn/TextConnections.java

...src/com/oracle/truffle/r/runtime/conn/URLConnections.java