[GR-2604] Implemented support for "raw" connections.

.../com/oracle/truffle/r/nodes/builtin/base/BasePackage.java

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

...le.r.runtime/src/com/oracle/truffle/r/runtime/RError.java

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

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

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

...cle/truffle/r/runtime/conn/SeekableMemoryByteChannel.java

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

...le/truffle/r/test/builtins/TestBuiltin_rawConnection.java

...ffle/r/test/builtins/connection/R/rawConnection_readBin.R

...r/test/builtins/connection/R/rawConnection_readWriteBin.R

...truffle/r/test/builtins/connection/R/rawConnection_seek.R

...fle/r/test/builtins/connection/R/rawConnection_writeBin.R