Make LowStar.BufferOps depend on LowStar.Modifies
Make LowStar.BufferOps depend on LowStar.Modifies

Suggested by @nikswamy; many people will forget about
LowStar.Modifies so let's have LowStar.BufferOps
depend on it to have the patterns into the SMT
context without polluting the F* scope.

FStarLang/FStar,A-Manning/FStar,FStarLang/FStar,FStarLang/FStar,A-Manning/FStar,A-Manning/FStar