bugfix: index label parsing code incorrect

bugfix: index label parsing code incorrect

Apparently split(/\s+/) is significantly different from split (which is
equivalent to split(" ")) in at least one case:

>> " a b  c   ".split(/\s+/)
=> ["", "a", "b", "c"]
>> " a b  c   ".split
=> ["a", "b", "c"]

This patch refactors the majority of uses of split(/\s+/) to a String#symbolize
method, which is correct.