We frequently use property name constants in conjunction with hash containers.
Provide new wrappers around apr_hash_get and apr_hash_set that accept such
string constants and statically determine their size.  That minimizes the
hash access costs.

Mass change hash get and set calls for SVN_PROP_* constants.

* subversion/include/svn_hash.h
  (svn_hash_gets,
   svn_hash_sets): Doxygen-ize the docstring
  (svn_hash_gets_fixed_key,
   svn_hash_sets_fixed_key): define new apr_hash_* wrapper

* subversion/libsvn_client/add.c
  (svn_client__get_all_auto_props): use faster hash wrappers with SVN_PROP_*

* subversion/libsvn_client/commit_util.c
  (svn_client__ensure_revprop_table): ditto

* subversion/libsvn_client/copy.c
  (repos_to_wc_copy_single): ditto

* subversion/libsvn_client/list.c
  (svn_client__ra_stat_compatible): ditto

* subversion/libsvn_client/log.c
  (pre_15_receiver): ditto

* subversion/libsvn_client/merge.c
  (prepare_merge_props_changed, merge_file_added, merge_dir_added,
   merge_dir_deleted): ditto

* subversion/libsvn_client/mergeinfo.c
  (svn_client__get_wc_or_repos_mergeinfo_catalog): ditto

* subversion/libsvn_fs_base/tree.c
  (txn_body_get_mergeinfo_data_and_entries,
   txn_body_get_mergeinfo_for_path): same

* subversion/libsvn_fs_fs/fs_fs.c
  (write_revision_zero): same

* subversion/libsvn_fs_fs/tree.c
  (crawl_directory_dag_for_mergeinfo, get_mergeinfo_for_path_internal): same

* subversion/libsvn_ra/deprecated.c
  (svn_ra_get_commit_editor2): same

* subversion/libsvn_ra_local/ra_plugin.c
  (svn_ra_local__get_commit_editor, svn_ra_local__get_commit_ev2): same

* subversion/libsvn_ra_svn/client.c
  (ra_svn_commit, ra_svn_log): same

* subversion/libsvn_repos/commit.c
  (svn_repos__get_commit_ev2): same

* subversion/libsvn_repos/delta.c
  (delta_proplists): same

* subversion/libsvn_repos/deprecated.c
  (svn_repos_get_commit_editor4): same

* subversion/libsvn_repos/dump.c
  (dump_node, write_revision_record): 

* subversion/libsvn_repos/fs-wrap.c
  (svn_repos_fs_begin_txn_for_commit2, svn_repos_fs_begin_txn_for_commit,
   svn_repos_fs_revision_proplist): same

* subversion/libsvn_repos/log.c
  (fill_log_entry): same

* subversion/libsvn_repos/reporter.c
  (get_revision_info): same

* subversion/libsvn_repos/rev_hunt.c
  (svn_repos_get_committed_info): same

* subversion/libsvn_subr/compat.c
  (svn_compat_log_revprops_clear, svn_compat_log_revprops_out): same

* subversion/libsvn_wc/status.c
  (collect_ignore_patterns): same

* subversion/mod_dav_svn/activity.c
  (dav_svn__create_txn): same

* subversion/mod_dav_svn/lock.c
  (append_locks): same

* subversion/svndumpfilter/svndumpfilter.c
  (output_revision): same

* subversion/svnmucc/svnmucc.c
  (execute, sanitize_log_sources): same

* subversion/svnrdump/load_editor.c
  (new_node_record): same

* subversion/svnserve/serve.c
  (commit): same

* subversion/svnsync/svnsync.c
  (replay_rev_started): same

git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1483532 13f79535-47bb-0310-9956-ffa450edef68