Fix for SuSE 9.0 2.4.21 kernel. Simplify jiffies_to_msecs() and

Fix for SuSE 9.0 2.4.21 kernel.  Simplify jiffies_to_msecs() and
msecs_to_jiffies() to avoid preprocessor optimisations that depend on
HZ being a C constant expression.  Just round the result up to the nearest
integer.  The supported range of input values (avoiding arithmetic overflow)
is now less than that of the Linux versions of these functions for common
values of HZ, but that's unlikely to cause any problems (and if it does we
can fix it by making the functions more complicated).