Don't reuse WebRequests on timeout

If a web request isn't able to complete within 15 seconds the
.Timeout observable would throw, making the .Retry kick into
action, re-scheduling the deferred request observable which
would throw if the web request was still running.

This makes sure we create a new web request on each retry.
Merge pull request #64 from github/no-webrequest-reuse-on-timeout

Don't reuse WebRequests on timeout in DownloadUrl
Revert "I'm feeling brave"

This reverts commit dd54e49d6a6cac73631efb9b17f4e2e07c63bd34, which only
happened to work sometimes not really.
Rewrite SQLiteConnectionPool

Now the pool itself handles queuing operations, based on
round-robin'ing a fixed number of connections
Fix all the operations

This also makes Reset properly signal completion
PersistentBlobCache should only know about AsyncConnection
Merge pull request #66 from github/fix-sqlite3-use

Fix parallel usage of Akavache SQLite3 connections
Added project targets hack for WP8 #67
Merge pull request #68 from PeteGoo/WP8_CacheInitialisation_Bug

Added project targets hack for WP8 #67
Update ext to the latest binaries
90% of .NET development is right clicking
Merge pull request #71 from github/update-ext

Move to official Reactive Extensions for Xamarin.*
Make our copy of SQLite3 internal

Other people are using the official or MVX versions of SQLite and we're
breaking them
NuGet package restore is build terrorism
Fix disposing connections in SQLite3 properly
Add an extra test to walk through object-related methods
Create blocking version of shutdown code as wrapper
I feel shame as a minor action
Attempt to unfuck error handling in SQLite.cs
Disable SQLite threading protection since we use our own