Pull latest code from upstream okhttp and okio

This change contains the OkHttp and Okio changes without
modification. The only additions are the
MODULE_LICENSE_APACHE2 files.

This corresponds closely to OkHttp 2.5.0 and
Okio 1.6.0. Behavior changes are documented in
CHANGELOG.md.

This change does not compile as is. The next
commit makes the Android modifications required.

okhttp: 4305dc3fabeab392eb56f2db51538e06c3a54e51
okio: 313436764bf35794e158c6171e319fee868298df

Change-Id: I97ce07ff0472cdbce09f588863a1e5ccdcea0c20
