Fix encoding of limit parameter value in webservice query (limit=%19)

This is a very old bug it seems, it was indirectly introduced by
commit 9092a7abcae5254e581497b346b2167a5e37cb26

The missing str() was causing integer value 25 to be encoded as
ascii char 25, then, after percent encoding, limit=%19 in the search url.
Merge pull request #197 from zas/fix_limit_encoding

Fix encoding of limit parameter value in webservice query (limit=%19)