Fix 1954

[fwesselm]

This PR fixes #1954:

1. Bound types of general-integer variables from variable bound constraints may have been overwritten, e.g. a variable upper bound of the form x <= b*y + c where x is NOT a continuous variable (for example, a general-integer variable) and y is a binary variable were not handled correctly.
2. Testing on 850+ MIPs (on Linux) showed that the fix affects behavior, but the overall results in terms of means of running times look reasonable.