Fix (false positive) pointer to int conversion warnings in FSX.

* subversion/libsvn_fs_x/noderevs.c
  (store_id): Use an intermediate for the hash contents and convert in
              a second step.
  (store_representation): Same.

* subversion/libsvn_fs_x/string_table.c
  (svn_fs_x__string_table_builder_add): Same.

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1619082 13f79535-47bb-0310-9956-ffa450edef68