RFR: 8025661: Ill-formed -Xminf and -Xmaxf options values interpreted as 0

[Stefan Johansson]

Hi,

Please review this fix for:
https://bugs.openjdk.java.net/browse/JDK-8025661

Webrev:
http://cr.openjdk.java.net/~sjohanss/8025661/webrev.00/

Summary:
The parsing of -Xminf and -Xmaxf has been done with atof() which doesn't 
detect errors. If using strtod() instead it's possible verify whether 
the whole input was parsed or not.

Also added a test to verify that we detect ill-formed input after the 
change.

Thanks,
StefanJ