Fix for nested parameters causing invalid signatures

[mhawkins]

I was trying to submit nested parameters (i.e. object[attribute]=value ) and was getting invalid signatures from our OAuth provider.

After tracing through the code, I saw that already encoded parameters were getting double encoded when submitted to HTTPParameter's getAsQueryString. In my branch, I modified SignatureBaseString's normalizeRequestParameters method to pass in decoded parameters to that method.

This resolved the problem for me. Thought I should pass this information back in case its of any use to you guys.