Speed-up FastCharsetProvider

[Ulf Zibis]

Hi Sherman, hi Martin,

I took a closer look to sun.io.cs.FastCharsetProvider, and found out, 
that there are some possibilities to enhance it.

I have filed a bug. See Review ID: 1425597 and:
https://java-nio-charset-enhanced.dev.java.net/source/browse/java-nio-charset-enhanced/trunk/src/sun/nio/cs/FastCharsetProvider.java?diff_format=s&rev=551&view=markup

-Ulf