Update base.js

Give users the index for properties. When I am rendering a radio button I use key-value pairs, but I can't use either as unique identifiers because they likely contain invalid identifier characters. I added "first" as an index as well, but have no particular use case for first. Since there is no way to detect "last", I didn't add that property.
Merge branch 'patch-1' of github.com:cgp/handlebars.js into cgp-patch-1
Use strict comparison for first
Add tests for object @index and @first handling