[option trws] new option for TRW-S in preprocessing ; kill several bugs about ToulBar2::costMultiplier and check multiplication overflow when loading the problem

[misc] reverted endSolve() to its initial signature + account for deltaUb in QPBO internally generated ub.

[bug] If an absolute gap is specified, only ub for true solutionsq/certificate can be shifted, niot initial Ubs.

[code] add variable and value label in solution printing -s option

[code] improve solution interprettion  -s optiion allows now to show  variable and value label when  -v=1 is used solution show var:value  info ; -v=2 show var:value:value index

[code] remove auto x{whatever} to avoid c++11 weirdness