fix #627: Merge SPDY settings when clear flag set. Revert Settings.DEFAULT_INITIAL_WINDOW_SIZE.
Fix problems with DeflaterSink.

We weren't checking Deflater.needsInput() in the deflate loop. This is
necessary on the RI, which returns 0 even when a subsequent call will
deflate data.
Merge pull request #628 from square/adrian.627

fix #627: merge SPDY settings when clear flag set.
Merge pull request #629 from square/jwilson_0310_deflatersink_close

Fix problems with DeflaterSink.
Fix problems with connection recycling and recovery.

We were incorrectly attempting to recycle connections terminated by the end
of a socket stream.

And we were keeping the 'Accept-Encoding: gzip' header on a recovered request,
which was suppressing our transparentGzip flag from getting the 'true' value
it requires.
Merge pull request #632 from square/jwilson_0310_recover_from_failures

Fix problems with connection recycling and recovery.
Document that OkHttpClient is thread-safe

While investigating a race-condition, I was momentarily worried when I
couldn't find any documentation actually stating that OkHttpClient is
thread-safe, apart from this Google+ post:

https://plus.google.com/118239425803358296962/posts/5nzAvPaitHu

...if I'm not the only person asking this question, probably best to
document it.
Doc: OkHttpClient need not /always/ be a singleton
Doc: OkHttpClient should be treated as immutable once shared

...given that requirement, it's safe for many threads to call the
open() method concurrently to open their own connections.

https://github.com/square/okhttp/pull/634#discussion_r10487815
Merge pull request #634 from rtyley/okhttpclient-is-threadsafe

Document that OkHttpClient is thread-safe
Changelog updates.
Merge pull request #636 from square/jwilson_0311_151_changelog

Changelog updates.
Empty line.
Don't double pool on a conditional cache hit.

We were pooling the unused connection twice, and the pool was getting two
copies of the same connection. Bad consequences followed.
Merge pull request #639 from square/jwilson_0311_dont_double_pool_on_cache_hit

Don't double pool on a conditional cache hit.
Fix a crash on conditional cache hits for new API.

Previously we were returning null when a 304 didn't validate. The problem
was caused by a bad test that specified Content-Length: 0 for a 304, which
isn't appropriate.
Sample: Crawler.
Merge pull request #637 from square/jwilson_0311_conditional_cache_miss

Fix a crash on conditional cache hits for new API.
Merge pull request #641 from square/jwilson/crawler

Sample: Crawler.
More 1.5 changes.