On the fsfs-format7 branch:  Make string tables easier to build
by copying the incoming strings into our builder-local pool.

* subversion/libsvn_fs_fs/string_table.c
  (svn_fs_fs__string_table_builder_add): copy strings before processing them

git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/fsfs-format7@1467365 13f79535-47bb-0310-9956-ffa450edef68