bug with indexed properties allowing access of elements on other indexed properties.

This request is for tests and code to address issue #230. 

When an indexed property is accessed, it retains the element definition and can be accessed from a different indexed property.

for example:
```
indexed_property :table, [
  [:div, :content, id: 'table[%s].content],
  [:div, :other_content, id: 'table[%s].other_content]
]

indexed_property :other_table, [
  [:div, :content, id: 'other_table[%s].content]
]
page.table['foo'].other_content
       #=> returns text from div_element(id: 'table[foo].other_content')
page.other_table['foo'].other_content
       #=> returns text from div_element(id: 'table[foo].other_content')
```
There are other repercussions as well. I've included 3 scenarios and a potential fix for the issue.