set single-device on profile-creation, assume multi-device when we go a hint

src/main/java/com/b44t/messenger/DcContext.java

@@ -236,6 +236,19 @@ public class DcContext {
       return getConfigInt("is_chatmail") == 1;
     }
 
+    // Called for new profiles on chatmail servers that are "single device" initially;
+    // to save server disk space, we make use of that delete all messages immediately after download.
+    public void assumeSingleDevice() {
+      setConfigInt("delete_server_after", 1 /*at once*/);
+    }
+
+    // Called when we get a hint that another device may be set up.
+    public void assumeMultiDevice() {
+      if (getConfigInt("delete_server_after") == 1 /*at once*/) {
+        setConfigInt("delete_server_after", 0 /*never/automatic*/);
+      }
+    }
+
     /**
      * @return true if at least one chat has location streaming enabled
      */

src/main/java/org/thoughtcrime/securesms/InstantOnboardingActivity.java

@@ -481,6 +481,9 @@ public class InstantOnboardingActivity extends BaseActionBarActivity implements
         return;
       }
       DcHelper.getAccounts(this).stopIo();
+      if (!isDcLogin) {
+        dcContext.assumeSingleDevice();
+      }
       dcContext.configure();
     }).start();
   }

src/main/java/org/thoughtcrime/securesms/WelcomeActivity.java

@@ -369,6 +369,7 @@ public class WelcomeActivity extends BaseActionBarActivity implements DcEventCen
             else if (progress==1000/*done*/) {
                 DcHelper.getAccounts(this).startIo();
                 progressSuccess();
+                dcContext.assumeMultiDevice();
                 notificationController.close();
                 cleanupTempBackupFile();
             }

src/main/java/org/thoughtcrime/securesms/preferences/ListSummaryPreferenceFragment.java

@@ -138,6 +138,7 @@ public abstract class ListSummaryPreferenceFragment extends CorrectedPreferenceF
   protected void startImexInner(int accountId, int what, String imexPath, String pathAsDisplayedToUser)
   {
     DcContext dcContext = DcHelper.getAccounts(getActivity()).getAccount(accountId);
+    dcContext.assumeMultiDevice();
     this.pathAsDisplayedToUser = pathAsDisplayedToUser;
     progressWhat = what;
     dcContext.imex(progressWhat, imexPath);

src/main/java/org/thoughtcrime/securesms/qr/BackupProviderFragment.java

@@ -64,6 +64,7 @@ public class BackupProviderFragment extends Fragment implements DcEventCenter.Dc
         progressBar.setIndeterminate(true);
 
         dcContext = DcHelper.getContext(getActivity());
+        dcContext.assumeMultiDevice();
         DcHelper.getEventCenter(getActivity()).addObserver(DcContext.DC_EVENT_IMEX_PROGRESS, this);
 
         prepareThread = new Thread(() -> {

src/main/java/org/thoughtcrime/securesms/qr/BackupReceiverFragment.java

@@ -94,6 +94,7 @@ public class BackupReceiverFragment extends Fragment implements DcEventCenter.Dc
             } else if (permille == 1000) {
                 getTransferActivity().setTransferState(BackupTransferActivity.TransferState.TRANSFER_SUCCESS);
                 getTransferActivity().doFinish();
+                dcContext.assumeMultiDevice();
                 return;
             }