STOCK PURCHASE AGREEMENT AMONG B&W EQUITY INVESTMENTS, LLC BABCOCK & WILCOX MEGTEC HOLDINGS, INC., BABCOCK & WILCOX MEGTEC, LLC, THE BABCOCK & WILCOX COMPANY, BABCOCK & WILCOX UNIVERSAL, INC., BABCOCK & WILCOX ENTERPRISES, INC., DURR INC., AND DÜRR...