Don't reset ridx,eidx. And fix for #1949

Conflicts:

	src/vm.c
OP_ENTER fix variable assignment
Make Array#[]= raise IndexError.

If second param is negative, Array#[] raise IndexError.
fix typo
Add tests for Range#to_s Range#inspect.
OP_ENTER clean block object in register
Add ISO No. to String#inspect test.
OP_ENTER fix segmentation fault
Change to raise TypeError (Hash#merge, #merge!)
Fix ISO No.
Add ISO No. to Integer#divmod  test.