RConnection#readLines gives more granular control over reported warnings

...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

...om/oracle/truffle/r/runtime/conn/DelegateRConnection.java

...acle/truffle/r/runtime/conn/DelegateWriteRConnection.java

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

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

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

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