Implement reading byref variants.

This commit is licensed under MIT/X11.
Merge pull request #623 from madewokherd/byrefvariants

Implement reading byref variants.
Add new net_4_5 class System.Web.MimeMapping
Fix support for reference types in unbox.any in gsharedvt code.
Merge pull request #624 from jbevain-forks/mimemapping

Add new net_4_5 class System.Web.MimeMapping
remove wrong EOLs after Libs: in reactive.pc.in. Third attempt to fix bug #10002.
Remove reflection usage to access NSTimeZone for iOS
Fix compilation of Variant for iOS: Marshal.GetObjectForIUnknown, like a lot of COM specific methods, is not available for iOS
[ios] throw an TimeZoneNotFoundException if the timezone name is unknown
Revert "Merge pull request #618 from knocte/aspnet_lru"

This reverts commit 675328ef1686ce884326df89f8c570943e2d20d2, reversing
changes made to edc181c514ddc082ce44cde69f2272a12e942b88.
NetworkChange: Support Mac OS X (bcx#12038)

Refactor System.Net.NetworkingInformation in order
to support multiple "providers"; previously only
Linux was ever supported for this API.

This patch provides basic support for Mac OS X
via the SystemConfiguration framework's
SCNetworkReachability API.

bxc#12038
Merge pull request #627 from abock/master

Support Mac OS X for System.Net.NetworkInformation.NetworkChange
mac-reachability.c: enable for TARGET_IOS
mac-reachability.c: update for C89isms

In response to Rodrigo's comments on PR 629.
Add PCL Facade assemblies.