RFR (JAXP) 8169450: StAX parse error if there is a newline in xml declaration

[huizhe wang]

A quick fix for the error parsing xml declaration. This is one of the 
three outstanding issues in the xml area that must be addressed for the 
coming development deadline.

JBS: https://bugs.openjdk.java.net/browse/JDK-8169450
webrev: http://cr.openjdk.java.net/~joehw/jdk9/8169450/webrev/

Checking whether a space follows "<?xml" was sufficient for DOM/SAX for 
which the base parser was originally created since the xml declaration 
was normalized during version detection. StAX, sharing the base parser 
after it was added to the JDK, however, does not use the same version 
detection/normalization process and would incorrectly parse the 
declaration if there are other whitespaces.

Thanks,
Joe