Make the @@constants Hash thread-safe by wrapping it in a Mutex

When multiple threads are creating instances of
Faraday::RackBuilder::Handler, the `@@constants` hash may exhibit
unexpected behaviour, as the Hash class is not thread-safe in Ruby.

This commit wraps all writes to `@@constants` in a Mutex, thereby
ensuring mutual exclusion.
fix net-http-persistent timeout detection on Ruby 2.0

Re-enable timeout test because drbrain/net-http-persistent#33 got fixed
in net-http-persistent 2.8
fix Typhoeus proxy support
prevent Typhoeus from using "Expect: 100-continue" on PUT

It seems whether the request method for Typhoeus request is `:put` or
"PUT" decides whether it will use "Expect: 100-continue" when performing
that request. In our test suite, such PUTs would fail randomly against
WEBrick which doesn't have stable support for 100 Continue. This seems
to be a problem with WEBrick, not Typhoeus.

This also speeds up these requests, which WEBrick was slow to process
even if they've succeeded.

"Expect: 100-continue" is a mode where the client sends this header, but
doesn't send the body of the request until the server inspects the
headers and decides it wants to allow the request by sending
"HTTP/1.1 100 Continue" back.
rewrite test script in bash

The HTTP server is now started in a subprocess, not a thread. Running it
in a Ruby thread had all sorts of problems on different Rubies, such as
random failures on Rubinius.

The new script also avoids starting the HTTP server if not needed, e.g.
if filtering arguments have been used to select only the non-adapter tests.

The script dumps the server log to stdout if any tests failed on Travis.

Avoids auto-starting the debugger because it blocks for input in Rubinius
https://travis-ci.org/lostisland/faraday/jobs/5956815
output the test server log if it fails to boot up
skip Typhoeus file upload test

Avoids random failures that happen in combination with WEBrick
Merge pull request #252 from leocassarani/constants-mutex

Make the @@constants Hash thread-safe by wrapping it in a Mutex
remove net_http_persistent todo

From the docs: "Multiple Net::HTTP::Persistent objects will share the same set of connections."

http://docs.seattlerb.org/net-http-persistent/Net/HTTP/Persistent.html
Loosen required_rubygems_version for compatibility with Ubuntu 10.04
Reset Faraday.default_connection on Faraday.default_adapter update
Merge pull request #265 from vijaykramesh/reset_default_connection_on_default_adapter_update

Reset Faraday.default_connection when setting Faraday.default_adapter
Merge pull request #261 from ajsharp/patch-1

remove net_http_persistent todo
hide bin if you use bundler and binstubs
Release 0.9.0.rc1
add a changelog
EM Synchrony should use Utils::URI
make the default uri parser configurable
allow Utils.default_uri_parser to take a URI object that responds to #parse
Merge pull request #267 from lostisland/configurable-URI

Configurable uri