Rewrite JROUND macro to multiply by 1e6 rather than divide by 1e-6

Rewrite JROUND macro to multiply by 1e6 rather than divide by 1e-6
 and vica versa for the next operation.
This is reputed to fix inline math optimization troubles in glibc-2.0.x.
Regression tests still pass on libc/i686 machine.  Patch suggested by Matt.