Old release 0.4.2 does not build

[ypeels]

Error output resulting from ant when building old release 0.4.2:

[javac]                     if (!metric.isThreadsafe()) {
[javac]                                ^
[javac]   symbol:   method isThreadsafe()
[javac]   location: variable metric of type Metric<?>
[javac] 1 error

Build succeeds after uncommenting the following line in src/multeval/metrics/Metric.java:

//public abstract boolean isThreadsafe();