[man] update Mono version from "2.11" to "3.0"
[WebConfigurationManager] Fix memleak by using a LruCache (BXC#5598)

System.Web.ConfigurationManager had a cache which didn't have any max limit,
therefore when using Restful URIs in ASP.NET (like having some variable
parameter in the virtual path, i.e. /user/{userId}/tracks, where {userId}
is a variable Integer) this was very likely to cause a leak which would
end up causing troubles, like an InvalidCastException thrown by
HttpApplication::PreStart()

(Read operations in the cache now cause a write operation on the cache
object, so all sectionCache lock-read usages are converted to lock-write.)

Fixes https://bugzilla.xamarin.com/show_bug.cgi?id=5598
[System.Web] Improve locking logic for WebConfigManager's sectionCache

As suggested by Marek Habersack, instead of catching
SynchronizationLockException in the case that the lock wasn't
acquired, we now have a boolean that indicates if it was
acquired or not, so we can act on it on the finally{} block.
Merge pull request #647 from knocte/aspnet_lru

[WebConfigurationManager] Fix memleak by using a LruCache (BXC#5598)