[PATCH] Clarify that 'svn patch' can only apply changes to targets that are dirs

Hi!

resolve_target_path() makes a few assumptions about the target for a
patch file beeing a wc_dir. Currently we can only invoke svn patch like
this:

  svn patch PATCH_FILE WC_DIR_PATH

Is this the intended behavoiour?

[[[

Make it clearer that the patch code can only use base paths that are
dirs.

* subversion/svn/main.c
  (svn_opt_subcommand_desc2_t): Clarify help text.

* subversion/include/svn_client.h
  (svn_client_patch): Replace parameter 'local_abspath' with
    'base_dir_abspath'.

* subversion/libsvn_client/patch.c
  (resolve_target_path,
   svn_client_patch): Replace parameter 'local_abspath' with
    'base_dir_abspath'
]]]
  
Cheers,
Daniel