Remove use of SortedSet.floor()

Its only available in Java 6, and JGit still supports Java 5.

Change-Id: I6c8fac06106ffe20ac8b4b595f34e027f2d29cc2
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

org.eclipse.jgit.test/tst/org/eclipse/jgit/treewalk/FileTreeIteratorWithTimeControl.java

@@ -43,6 +43,7 @@
 package org.eclipse.jgit.treewalk;
 
 import java.io.File;
+import java.util.SortedSet;
 import java.util.TreeSet;
 
 import org.eclipse.jgit.lib.ObjectReader;
@@ -98,8 +99,8 @@ public class FileTreeIteratorWithTimeControl extends FileTreeIterator {
 
 	@Override
 	public long getEntryLastModified() {
-		Long cutOff = modTimes
-				.floor(Long.valueOf(super.getEntryLastModified()));
-		return (cutOff == null) ? 0 : cutOff;
+		Long cutOff = Long.valueOf(super.getEntryLastModified());
+		SortedSet<Long> head = modTimes.headSet(cutOff);
+		return head.isEmpty() ? 0 : head.last().longValue();
 	}
 }