[Cbc] Semi-continuous/SOS/.LP format

[John Forrest]

1) Reading .lp format (by the way this is Cplex .lp format) has been 
improved.  The code throws an error in same cases - this is now trapped 
and the error message printed.
2) .lp format allowed Set1 S1:: (with a space) - this failed with Cbc.
3) Semi-continuous hopefully better.
4) SOS - in the failing example given, the continuous relaxation was 
(correctly) unbounded - Cbc does not like this.  My simple fix is to 
automatically reduce bounds to -1.0e15/+1.0e15 - if your objective is 
dollars then this is still serious money.
5) Some bugs in preprocessing with semi-continuous/SOS.

All in trunk - I hope it helps.

John Forrest