Fix #20, Support for custom TrustManagers

 * renamed trustAllManagers to TrustManagers to reflect that
   this isn't necessary an all-accepting TrustManager anymore
 * added installCustomTrustManager() to XMLRPCClient
 * with FLAGS_SSL_IGNORE_INVALID_CERT set a custom TrustManager
   is overridden by the all-accepting version.
Minor optimizations at TrustManagers
Prepared v1.7.0