Previous check-in accidently left mmap turned off by default. This checkin

fixes that.  Unfortunately, shared.test is now segfaulting.  All other
veryquick tests appear to work, however.

FossilOrigin-Name: a850c7319c20b5757983443df05cf2aa4250053b

src/pager.c

@@ -4749,6 +4749,7 @@ int sqlite3PagerOpen(
   /* pPager->pBusyHandlerArg = 0; */
   pPager->xReiniter = xReinit;
   /* memset(pPager->aHash, 0, sizeof(pPager->aHash)); */
+  pPager->mxMmap = SQLITE_DEFAULT_MMAP_LIMIT;
 
   *ppPager = pPager;
   return SQLITE_OK;