[Clp] Coefficient for slack variables

[Giacomo Nannicini]

Hi,
I noticed that the default coefficient for slack variables in
CoinFactorization has changed from +1 to -1 in the latest versions of
the code (can be found in CoinFactorization::slackValue_), but it also
depends on the define COIN_FAST_CODE.
Is there a reason for this? I noticed that if COIN_FAST_CODE is
defined, the default is +1. So, is the +1 option faster?

Thanks

Giacomo