Added support for HTTP_PROXY and HTTPS_PROXY environment variables, if the proxy option isn't already set.
Won't use HTTP(S)_PROXY env var if proxy explicitly set to null.
defaults: merge headers
prefer late return statement
check for content-length header before setting it in nextTick
Merge pull request #951 from kevinoid/content-decoding

Add support for gzip content decoding
Silence EventEmitter memory leak warning #311

When performing a lot of concurrent requests on a keep-alive connection, a lot of error handlers can be added, which in turn will result in the following warning: "possible EventEmitter memory leak detected. 11 listeners added". This isn't really a memory leak and should just be silenced.
Merge pull request #955 from camilleanne/master

check for content-length header before setting it in nextTick
Merge pull request #957 from watson/master

Silence EventEmitter memory leak warning #311
Fixing for 0.8
2.37.0
2.37.1
Merge pull request #946 from aj0strow/merge-default-headers

defaults: merge headers
Merge pull request #844 from jvmccarthy/issue595_http_proxy_env_vars

Add support for HTTP[S]_PROXY environment variables.  Fixes #595.
Support gzip with encoding on node pre-v0.9.4

setEncoding was added to zlib streams in joyent/node@9b5abe5 (v0.9.4 and
later).  In order to support encoding and gzip together on earlier
releases, pass the data through an additional Stream which decodes the
data using the stringstream module.

Signed-off-by: Kevin Locke <kevin@kevinlocke.name>