Additional tidy up in timeman.cpp

Simplified the ratio formulas and verified
that after int conversion there is no difference:

assert(int(myTime * ratio_old) == int(myTime * ratio_new));

With big numbers of myTime. Actually the difference
(ratio_old - ratio_new) is on the order of 0.1e-15
and all due to rounding errors.

Also fixed some comments and moved/renamed some
variables.

No functional change.