Add Persistent#max_requests to prevent ECONNRESET

 * Many servers have a max_requests tunable on keepalive connections that is
   tuned to less than infinite. Some of these servers incorrectly close the
   connection out-of-band (rather than replying with Connection:close). In these
   cases, it is advantageous to avoid the resulting ECONNRESET, and preemptively
   reset those connections.
 * Additional potential work that could be done later: Make a closing request on
   the last request. Add a detect_max_requests helper at the top level.
 * Exmaple configuration link:
   http://wiki.nginx.org/HttpCoreModule#keepalive_requests
Use lowercase HTTP proxy env variables to avoid warning
Finish connections for unhandled exceptions

When an exception that is otherwise not retried occurs
net-http-persistent did not finish the connection.  This could leave
the server response outstanding on the connection resulting in the
response for a pre-exception request A being delivered to a
post-exception request B.

Issue #46
Merge pull request #42 from raggi/max_requests

Add Persistent#max_requests to prevent ECONNRESET
Added #42 to history
Use minitest 5 classes
Fix comparison order for #42

Noted by Roman Shterenzon
Make autotest only listen to test dependencies
On request failure, raise with original backtrace

This allows users to get a better idea of why they see the "too many
connection resets" errors.

See #41
SSLReuse is only available with OpenSSL
Add backtrace change to History
Assume StandardError means the connection timed out

Fixes #43
Use ruby 2.0.0 instead of ruby-head
Set release date
Merge drbrain/net-http-persistent@v2.9 into gemspec2