[GR-4099] Polish grid support in FastR.

...y/src/com/oracle/truffle/r/library/fastrGrid/LRaster.java

.../r/library/fastrGrid/device/awt/BufferedJFrameDevice.java

...ffle/r/library/fastrGrid/device/awt/Graphics2DDevice.java

.../truffle/r/library/fastrGrid/device/awt/JFrameDevice.java

...e/truffle/r/library/fastrGrid/grDevices/DevHoldFlush.java

...le/truffle/r/library/fastrGrid/graphics/R/fastrGraphics.R

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

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

.../oracle/truffle/r/test/builtins/TestBuiltin_asvector.java