Really accept all certificates in Java 7

In Java 7, a new X509ExtendedTrustManager class is introduced and the old
X509TrustManager implementations are wrapped in
`src/share/classes/sun/security/ssl/SSLContextImpl.java` using
`AbstractTrustManagerWrapper`. This class always checks the algorithm
constraints which may therefore reject some certificates that are signed with
an insecure algorithm (for example, MD2withRSA). By providing a full
X509ExtendedTrustManager implementation, this wrapper is not used and all
certificates get accepted.

Note: Java 6 does not have a X509ExtendedTrustManager class.
Provide a dummy X509ExtendedTrustManager

Java 6 does not have the X509ExtendedTrustManager class, but since
ClientTrustedManager needs to be extended from it in Java 7 a compatibility
class needs to be shipped with Java 6.