Kernel+Userland: Implement fchmod() syscall and use it to improve /bin/cp.

/bin/cp will now copy the permission bits from source to destination. :^)

Kernel/FileDescriptor.cpp

@@ -138,6 +138,13 @@ int FileDescriptor::fstat(stat* buffer)
     return 0;
 }
 
+KResult FileDescriptor::fchmod(mode_t mode)
+{
+    if (!m_inode)
+        return KResult(-EBADF);
+    return VFS::the().chmod(*m_inode, mode);
+}
+
 off_t FileDescriptor::seek(off_t offset, int whence)
 {
     ASSERT(!is_fifo());