Fix a subtle cache inefficiency in 1.8 (does not exist in 1.7):
When using a struct as cache key, its content cannot always be
initialized by assigning all members.  Due to data alignment,
4 of the 16 bytes in pair_cache_key_t will have random content
if its first member (a long) is 4 instead 8 bytes long.

* subversion/libsvn_fs_fs/fs_fs.c
  (get_cached_node_revision_body,
   set_cached_node_revision_body,
   parse_revprop,
   get_revision_proplist,
   read_representation,
   svn_fs_fs__try_process_file_contents, 
   svn_fs_fs__get_proplist): explicitly initialize the *whole* key

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1442058 13f79535-47bb-0310-9956-ffa450edef68