Refactor wal.c to use the VFS.  This check-in compiles and links and works
ok as long as you leave WAL turned off, but WAL does not work.

FossilOrigin-Name: 62db5fa3b61be885b2d94e9b9ce3877b2c588350
diff --git a/src/vdbeapi.c b/src/vdbeapi.c
index 1c938ee..12100ce 100644
--- a/src/vdbeapi.c
+++ b/src/vdbeapi.c
@@ -306,15 +306,15 @@
   pCtx->s.db->mallocFailed = 1;
 }
 
-static int doLogCallbacks(sqlite3 *db){
+static int doWalCallbacks(sqlite3 *db){
   int i;
   int rc = SQLITE_OK;
   for(i=0; i<db->nDb; i++){
     Btree *pBt = db->aDb[i].pBt;
     if( pBt ){
-      int nEntry = sqlite3PagerLogCallback(sqlite3BtreePager(pBt));
-      if( db->xLogCallback && nEntry>0 && rc==SQLITE_OK
-       && db->xLogCallback(db->pLogArg, db, db->aDb[i].zName, nEntry)
+      int nEntry = sqlite3PagerWalCallback(sqlite3BtreePager(pBt));
+      if( db->xWalCallback && nEntry>0 && rc==SQLITE_OK
+       && db->xWalCallback(db->pWalArg, db, db->aDb[i].zName, nEntry)
       ){
         rc = sqlite3PagerCheckpoint(sqlite3BtreePager(pBt));
       }
@@ -406,7 +406,7 @@
 
   if( rc==SQLITE_DONE ){
     assert( p->rc==SQLITE_OK );
-    p->rc = doLogCallbacks(db);
+    p->rc = doWalCallbacks(db);
     if( p->rc!=SQLITE_OK ){
       rc = SQLITE_ERROR;
     }