* Basically Field#to_param was replaced for Field#to_query_string and
some methods related to build params were moved to Form class.
Before this commit the params hash was made by parsing each element
querystring to param and then merge, now we build the whole querystring
first and then parse it to get params with Rack or Rails depending of
the configure mode.
Mechanize takes input as plaintext and escapes field values on its own.
If the values are escaped before they are passed to Mechanize, the values will be escaped twice.
These doubly-escaped values will result in incorrect behavior on the server side.
