Bump watch anti-entropy

There have been reports that often a new build will be triggered
immediately after the previous build even when none of the files have
been modified since the start of the last build. This can happen when,
for example, a program implements save with a rename. When that occurs,
a deletion watch event may trigger the build but the corresponding
creation event may be detected outside of the current 40ms window. By
bumping this value to 500ms, we hopefully prevent the majority of these
false triggers. For unusual workflows in which this longer quarantine
period is an issue, the setting can be overridden.

main/src/main/scala/sbt/Defaults.scala

@@ -264,7 +264,7 @@ object Defaults extends BuildCommon {
       concurrentRestrictions := defaultRestrictions.value,
       parallelExecution :== true,
       pollInterval :== new FiniteDuration(500, TimeUnit.MILLISECONDS),
-      watchAntiEntropy :== new FiniteDuration(40, TimeUnit.MILLISECONDS),
+      watchAntiEntropy :== new FiniteDuration(500, TimeUnit.MILLISECONDS),
       watchService :== { () =>
         Watched.createWatchService()
       },