add "http://" scheme to ENV['http_proxy'] value if missing

This allows:

    http_proxy=localhost:8888 ruby myscript.rb

Omitting the scheme is already supported by curl, and this matches that
behavior.
remove obsolete comment for net-http-persistent

net-http-persistent maintains an internal connection pool which it
shares among instances. Therefore it's safe to create new instances of
Net::HTTP::Persistent.
don't swallow exceptions in em-synchrony
ensure consistent handling of connection failures

All adapters should now raise Faraday::Error::ConnectionFailed
add HTTP proxy authentication support to EM adapters
add HTTP proxy support for Excon
fix HTTP proxy authentication for Patron
fix HTTP proxy authentication for net-http-persistent

Because net-http-persistent 2.8 doesn't unescape `user/password` values,
we override those accessors on the URI instance to return raw values.

References drbrain/net-http-persistent#48
consistently handle 407 Proxy Authentication Required for HTTPS requests
handle a special-case of connection failed with EM

https://travis-ci.org/lostisland/faraday/jobs/9489250
bump jruby-openssl to fix hang issues

It would hang indefinitely for HTTPS requests from JRuby 1.7.4 on my Mac
have script/server log to stdout when called directly
add integration tests for HTTP proxy support

Spins up a proxy server in a separate process, runs a few requests
through it with each adapter to verify that both proxy support and basic
authentication take effect.
ignore Rubinius crashes

I cannot figure it out; I give up
bump multipart-post dependency for Ruby 2.0 compatibility
fix multipart post for servers that choke on Content-Type

Some servers such as Exchange 2010 don't like that there isn't a space
after a semicolon separator in the Content-Type request header. Since
Net::HTTPHeader#set_content_type adds the space, as well as it appearing
in the examples of RFC 2616, this follows suit and adds a space which
should help bad-behaving servers and not harm others.
Release 0.8.8