RFR 6856817: Poor performance of Writer#append with CharBuffer

[vyom]

Hi All,

Please review my changes for below bug.
Bug:        JDK-6856817 : Poor performance of Writer#append with CharBuffer
Webrev: http://cr.openjdk.java.net/~vtewari/6856817/webrev0.4/ 
<http://cr.openjdk.java.net/%7Evtewari/6856817/webrev0.4/>

This change will avoid the redundant toString/CharBuffer.wrap in case of 
OutputStreamWriter.append(CharBuffer).

In case of OutputStreamWriter.append(CharBuffer) we are doing 
CharBuffer->String->char[]->CharBuffer conversion this change will avoid 
redundant conversion.

Thanks,
Vyom