promote HandshakeSettings._filter() to public

since the _filter is used outside its class, it should be
a public method. The `filter` is a reserved word though, so
rename the method to `validate()`.

tlslite/handshakesettings.py

@@ -111,9 +111,15 @@ def __init__(self):
         self.useExperimentalTackExtension = False
         self.sendFallbackSCSV = False
 
-    # Validates the min/max fields, and certificateTypes
-    # Filters out unsupported cipherNames and cipherImplementations
-    def _filter(self):
+    def validate(self):
+        """
+        Validate the settings, filter out unsupported ciphersuites and return
+        a copy of object. Does not modify the original object.
+
+        @rtype: HandshakeSettings
+        @return: a self-consistent copy of settings
+        @raise ValueError: when settings are invalid, insecure or unsupported.
+        """
         other = HandshakeSettings()
         other.minKeySize = self.minKeySize
         other.maxKeySize = self.maxKeySize

tlslite/tlsconnection.py

@@ -370,7 +370,7 @@ def _handshakeClientAsyncHelper(self, srpParams, certParams, anonParams,
         # or crypto libraries that were requested        
         if not settings:
             settings = HandshakeSettings()
-        settings = settings._filter()
+        settings = settings.validate()
 
         if clientCertChain:
             if not isinstance(clientCertChain, X509CertChain):
@@ -1116,7 +1116,7 @@ def _handshakeServerAsyncHelper(self, verifierDB,
 
         if not settings:
             settings = HandshakeSettings()
-        settings = settings._filter()
+        settings = settings.validate()
 
         # OK Start exchanging messages
         # ******************************