Avoid parsing the hooks-env file with every hook invocation by caching
the results of the first such parsing in the svn_repos_t.

* subversion/libsvn_repos/repos.h
  (svn_repos_t): Add 'hooks_env' member.

* subversion/libsvn_repos/hooks.c
  (parse_hooks_env): Lose 'result_pool' and 'local_abspath'
    parameters; add 'repos'.  Now consult/populate a cache of this
    hooks-env data found in the svn_repos_t object.
  (svn_repos__hooks_start_commit,
   svn_repos__hooks_pre_commit,
   svn_repos__hooks_post_commit,
   svn_repos__hooks_pre_revprop_change,
   svn_repos__hooks_post_revprop_change,
   svn_repos__hooks_pre_lock,
   svn_repos__hooks_post_lock,
   svn_repos__hooks_pre_unlock,
   svn_repos__hooks_post_unlock): Update calls to parse_hooks_env().


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1464079 13f79535-47bb-0310-9956-ffa450edef68