RFR: JDK-8200363 Add javadoc command line setting to fail on warnings

[Jonathan Gibbons]

Please review a simple change to (finally) implement the long-overdue 
-Werror option.

The existing undocumented -Xwerror option is repurposed and renamed, and 
its behavior modified to match the javac -Werror option.  The old name 
is retained as a alias "for a while" but since it is an undocumented 
option it may be removed at any time, and perhaps in the next release 
after this change (i.e. 16.)

In the resource file, an unused property is removed, and an error 
(mismatched braces) is fixed in another.

-- Jon

JBS: https://bugs.openjdk.java.net/browse/JDK-8200460
Webrev: http://cr.openjdk.java.net/~jjg/8200363/webrev.00/