RFR(S): JDK-8214444: Wrong strncat limits in dfa.cpp

[Dmitry Chuyko]

Hello,

Please review a small fix for another error found by modern GCC. 
strncat()-s with wrong limits are replaced by snprintf()-s. For VS2013 
compatibility there is additional define and force null termination.

bug: https://bugs.openjdk.java.net/browse/JDK-8214444
webrev: http://cr.openjdk.java.net/~dchuyko/8214444/webrev.00/
testing: submit repo

-Dmitry