cannot request paths containing escaped slash, i.e. '/api/exchanges/%2f/amq.direct'

[joshgontijo]

From #160

Trying to access the RabbitMO management API, I figured out, that it is impossible to send a request to an URL containing an escaped slash '/', i.e. '/api/exchanges/%2f/amq.direct'
That's mainly because the java URI(scheme,...,...) constructor would do a toString() first qouting/escaping all parameters and than parse the resulting string; during the toString() however the path is quoted/encoded, so a a string like '%2f' is written out as '%252f'.
And specifying the path as '/api///whatever' is not a solution either, as the '/' is valid path character, and does not get escaped.

One might surely argue, that this is Java URI problem, however it prevents unirest-java to be used with URIs containing an escaped '/'.

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Inside com.mashape.unirest.http.HttpClientHelper method prepareRequest, the URL is split up into an URI where the path is url-decoded. This url-decoding seems not correct.
For me it creates
http://host/v1/guid//test/tree
from
http://host/v1/guid/%2Ftest/tree
which then leads to a 404 on the server.

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