7036021: G1: build failure on win64 and linux with hs21 in jdk6 build environment
Summary: Missing parentheses around a casted expression and some missing casts were causing build failures with the jdk6 build tools.
Reviewed-by: kvn, brutisso
7036482: clear argument is redundant and unused in cardtable methods
Summary: Removed the unused clear argument to various cardtbale methods and unused mod_oop_in_space_iterate method. Unrelated to synopsis, added a pair of clarifying parens in AllocationStats constructor.
Reviewed-by: brutisso, jcoomes