Downgrade bdb to 5.3.28

bdb 6.X was released under the AGPL, which is incompatible with MIT-licensed
software (the result must be licensed under AGPL). bdb 5.X uses the same license
as bdb 4.8, and thus retains the same compatibility as in upstream Bitcoin.

Thanks to Luke-Jr for raising this issue.

configure.ac

@@ -263,9 +263,9 @@ case $host in
          dnl add default macports paths
          CPPFLAGS="$CPPFLAGS -isystem /opt/local/include"
          LIBS="$LIBS -L/opt/local/lib"
-         if test -d /opt/local/include/db62; then
-           CPPFLAGS="$CPPFLAGS -I/opt/local/include/db62"
-           LIBS="$LIBS -L/opt/local/lib/db62"
+         if test -d /opt/local/include/db53; then
+           CPPFLAGS="$CPPFLAGS -I/opt/local/include/db53"
+           LIBS="$LIBS -L/opt/local/lib/db53"
          fi
        fi
 
@@ -512,7 +512,7 @@ AC_SUBST(LIBMEMENV)
 
 if test x$enable_wallet != xno; then
     dnl Check for libdb_cxx only if wallet enabled
-    BITCOIN_FIND_BDB62
+    BITCOIN_FIND_BDB53
 fi
 
 dnl Check for libminiupnpc (optional)