RFR (S) 8230338 : Accurate error message about bad Unicode block name

[Ivan Gerasimov]

Hello!

When Pattern.compile complains about a wrong Unicode block name, it 
includes the prefix "In" twice, like this:
''Unknown character property name {*In*/Is*In*BadBlockName} near index NN ''

Would you please help review a trivial fix, which makes the message more 
accurate?

BUGURL: https://bugs.openjdk.java.net/browse/JDK-8230338
WEBREV: http://cr.openjdk.java.net/~igerasim/8230338/00/webrev/

Thanks in advance!

-- 
With kind regards,
Ivan Gerasimov