Mention deprecation of runtime_prepend_subdirectories
pathogen.vim 2.1

* Deprecate :Vopen commands in favor of scriptease.vim.
* Deprecate pathogen#infect() calls on paths without explicit globs.
* Introduce pathogen#incubate().
* Deprecate pathogen#runtime_append_all_bundles().
* Introduce pathogen#surround().
* Deprecate pathogen#runtime_prepend_subdirectories().
* Allow absolute paths in g:pathogen_disabled.