Add spec for Range#each when Symbol elemenets on X19
Fix Range#each for multi-character Symbol elements. Fixes #2149
Simplify Range#each for String elements
Adjust Range#each for X18

Ruby 1.8.7 can not generate Range objects from Symbol elements

:a..:b #=> ArgumentError: bad value for range

This commit removes verbose dealing for Symbol on X18
Merge pull request #2150 from kachick/fix_improve-range_each

Fix Range#each for Symbol elements and some simplifications