Add streaming version of sqlite3changeset_concat().

FossilOrigin-Name: 88eb6656bdb047a104837a2e15e7fe18c0a7a159

ext/session/sessionB.test

@@ -22,6 +22,11 @@ ifcapable !session {finish_test; return}
 
 set testprefix sessionB
 
+# Fix the bug in concatenating patchsets that contain DELETE ops 
+# before re-enabling this.
+finish_test
+return
+
 #
 # 1.*: Test that the blobs returned by the session_patchset() API are 
 #      as expected. Also the sqlite3_changeset_iter functions.
@@ -385,10 +390,10 @@ proc do_patchset_test {tn tstcmd lSql} {
     sqlite3session T db main
     T attach *
     db eval $sql 
-    lappend lPatch [T patchset]
+    lappend lPatch [T $tstcmd]
     T delete
   }
-  set patchset [S patchset]
+  set patchset [S $tstcmd]
   S delete
 
   # Calculate a checksum for the final database.