Re-enable modernized version of "optional" SSL/TLS

* Add "Accept all certificates" modes to incoming/outgoing secure choices
* Change URI scheme slightly to make "trust" a flag, not part of the
    protocol.
* Change Stores to know about new URI scheme
* Slightly rework Transport API to make "trust" an independent flag
* Adapt HostAuth to handle new Uri scheme
* Remove the old ambiguous "optional" code, which was allowing
    some unsigned certificates, but was *also* allowing TLS to
    optionally start (though not SSL, despite the UI strings.)
* Add a few unit tests to EmailContent
* Add logging and a bunch of comments to TrustManagerFactory, and a bit
    of simple cleanup to make it more readable.
* Add missing conversion of SSLException->CertificateValidationException
    in TLS so we get the correct certificate errors from TLS too.
* Re-enable TLS for mac.com accounts (which had a certificate problem)

Fixes bug http://b/2119755, http://b/1374780, and probably a raft of
earlier and/or external bugs about certificate problems.

Change-Id: Iaf99a8da3eaadaa4cdeec224737838b5d6813e55
diff --git a/res/values/strings.xml b/res/values/strings.xml
index b2c77cd..ba2a9e0 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -32,7 +32,10 @@
     <string name="special_mailbox_display_name_sent"></string>
     <!-- Do Not Translate.  Unused string. -->
     <string name="special_mailbox_display_name_junk"></string>
-
+    <!-- Do Not Translate.  Unused string. -->
+    <string name="account_setup_incoming_security_ssl_optional_label"></string>
+    <!-- Do Not Translate.  Unused string. -->
+    <string name="account_setup_incoming_security_tls_optional_label"></string>
 
     <!-- Permissions label for reading attachments -->
     <string name="read_attachment_label">Read Email attachments</string>
@@ -362,13 +365,13 @@
     <!-- "Incoming server settings" screen, options for "Security type" pop-up menu -->
     <string name="account_setup_incoming_security_none_label">None</string>
     <!-- "Incoming server settings" screen, options for "Security type" pop-up menu -->
-    <string name="account_setup_incoming_security_ssl_optional_label">SSL (if available)</string>
+    <string name="account_setup_incoming_security_ssl_trust_certificates_label">SSL (Accept all certificates)</string>
     <!-- "Incoming server settings" screen, options for "Security type" pop-up menu -->
-    <string name="account_setup_incoming_security_ssl_label">SSL (always)</string>
+    <string name="account_setup_incoming_security_ssl_label">SSL</string>
     <!-- "Incoming server settings" screen, options for "Security type" pop-up menu -->
-    <string name="account_setup_incoming_security_tls_optional_label">TLS (if available)</string>
+    <string name="account_setup_incoming_security_tls_trust_certificates_label">TLS (Accept all certificates)</string>
     <!-- "Incoming server settings" screen, options for "Security type" pop-up menu -->
-    <string name="account_setup_incoming_security_tls_label">TLS (always)</string>
+    <string name="account_setup_incoming_security_tls_label">TLS</string>
     <!-- "Incoming server settings" screen, label for pop-up menu -->
     <string name="account_setup_incoming_delete_policy_label">Delete email from server</string>
     <!-- "Incoming server settings" screen, options in pop-up menu for Delete email from server: -->