fix #661 simplify array subscript access nil check
BasicObject#method_missing works after removal

Specs fixed:

BasicObject
- raises NoMethodError for nonexistent methods after #method_missing is removed
Merge pull request #698 from kostya/subscript

fix #661 simplify array subscript access nil check
Merge pull request #701 from krekoten/bo_method_missing

BasicObject#method_missing works after removal