Work around platform differences in the directory watcher test.

- Drops all events that happen before any changes are made (FSEventStream reports events from the past to a certain degree)
- Tests the same file twice in a row, since FSEventStream might coalesce events and report bogus changes
- Allows "modified" instead of "added" events, because FSEventStream does not allow to distinguish in some cases

tests/0-dirwatcher-rec.d

@@ -35,13 +35,15 @@ void main()
 	// test non-recursive watcher
 	watcher = eventDriver.watchers.watchDirectory(testDir, false, toDelegate(&testCallback));
 	assert(watcher != WatcherID.invalid);
-	Thread.sleep(400.msecs); // some watcher implementations need time to initialize
+	// some watcher implementations need time to initialize or report past events
+	dropChanges(2000.msecs);
 	testFile(     "file1.dat");
 	testFile(     "file2.dat");
 	testFile(     "dira/file1.dat", false);
 	testCreateDir("dirb");
 	testFile(     "dirb/file1.dat", false);
 	testRemoveDir("dirb");
+	testFile(     "file1.dat");
 	eventDriver.watchers.releaseRef(watcher);
 	testFile(     "file1.dat", false);
 	testRemoveDir("dira", false);
@@ -50,7 +52,8 @@ void main()
 	// test recursive watcher
 	watcher = eventDriver.watchers.watchDirectory(testDir, true, toDelegate(&testCallback));
 	assert(watcher != WatcherID.invalid);
-	Thread.sleep(400.msecs); // some watcher implementations need time to initialize
+	// some watcher implementations need time to initialize or report past events
+	dropChanges(2000.msecs);
 	testFile(     "file1.dat");
 	testFile(     "file2.dat");
 	testFile(     "dira/file1.dat");
@@ -58,6 +61,7 @@ void main()
 	testFile(     "dirb/file1.dat");
 	testRename(   "dirb", "dirc");
 	testFile(     "dirc/file2.dat");
+	testFile(     "file1.dat");
 	eventDriver.watchers.releaseRef(watcher);
 	testFile(     "file1.dat", false);
 	testFile(     "dira/file1.dat", false);
@@ -78,11 +82,30 @@ void testCallback(WatcherID w, in ref FileChange ch)
 	pendingChanges ~= ch;
 }
 
+void dropChanges(Duration dur)
+{
+	auto starttime = MonoTime.currTime();
+	auto remdur = dur;
+	while (remdur > 0.msecs) {
+		auto er = eventDriver.core.processEvents(remdur);
+		switch (er) {
+			default: assert(false, format("Unexpected event loop exit code: %s", er));
+			case ExitReason.idle: break;
+			case ExitReason.timeout: break;
+			case ExitReason.outOfWaiters:
+				assert(false, "No watcher left, but expected change.");
+		}
+		remdur = dur - (MonoTime.currTime() - starttime);
+	}
+
+	pendingChanges = null;
+}
+
 void expectChange(FileChange ch, bool expect_change)
 {
 	auto starttime = MonoTime.currTime();
 	again: while (!pendingChanges.length) {
-		auto er = eventDriver.core.processEvents(10.msecs);
+		auto er = eventDriver.core.processEvents(100.msecs);
 		switch (er) {
 			default: assert(false, format("Unexpected event loop exit code: %s", er));
 			case ExitReason.idle: break;
@@ -123,9 +146,12 @@ void expectChange(FileChange ch, bool expect_change)
 	if (pch.kind == FileChangeKind.modified && (pch.name == "dira" || pch.name == "dirb"))
 		goto again;
 
-	// test all field excep the isDir one, which does not work on all systems
+	// test all field except the isDir one, which does not work on all systems
-	assert(pch.kind == ch.kind && pch.baseDirectory == ch.baseDirectory &&
+	// we allow "modified" instead of "added" here, as the FSEvents based watcher
-		pch.directory == ch.directory && pch.name == ch.name,
+	// has strange results on the CI VM
+	assert((pch.kind == ch.kind || pch.kind == FileChangeKind.modified && ch.kind == FileChangeKind.added)
+		&& pch.baseDirectory == ch.baseDirectory
+		&& pch.directory == ch.directory && pch.name == ch.name,
 		format("Unexpected change: %s vs %s", pch, ch));
 }