Adds support for PKCS12 containers to SecurityContext

CHANGELOG.md

 ## 1.15.0
 
 ### Core library changes
   * Added `Uri.queryParametersAll` to handle multiple query parameters with
     the same name.
 
 * `dart:io`
   * Added `SecurityContext.usePrivateKeyBytes`,
           `SecurityContext.useCertificateChainBytes`,
           `SecurityContext.setTrustedCertificatesBytes`, and
           `SecurityContext.setClientAuthoritiesBytes`.
   * The non-`Bytes` methods of `SecurityContext` are being renamed -`Sync`, as
     they will do synchronous IO. The non-`Bytes` and non-`Sync` methods are
     deprecated and will be removed in a later release.
   * **Breaking** The named `directory` argument of
     `SecurityContext.setTrustedCertificates` is no longer supported.
     The method now only supports one argument for the PEM file name containing
     the trusted certificates.
+  * Added support to SecurityContext for PKCS12 certificate and key containers.
 
 ## 1.14.1 - 2016-02-04
 
 Patch release, resolves one issue:
 
 * Debugger: Fixes a VM crash when a debugger attempts to set a break point
 during isolate initialization.
 (SDK issue [25618](https://github.com/dart-lang/sdk/issues/25618))
 
 ## 1.14.0 - 2016-01-28
@@ skipping 752 matching lines @@
     they will keep the Dart process alive until they time out. This fixes the
     handling of persistent connections. Previously, the client would shut down
     immediately after a request.
 
   * **Breaking change:** `HttpServer` no longer compresses all traffic by
     default. The new `autoCompress` property can be set to `true` to re-enable
     compression.
 
 * `dart:isolate`: `Isolate.spawnUri` added the optional `packageRoot` argument,
   which controls how it resolves `package:` URIs.