Parallels the commit to apr.h.in/apr.hw for the apache core library.

  Parallels the commit to apr.h.in/apr.hw for the apache core library.
  Only mod_dav/mod_dav_fs and ap_hooks.h (as best examples) will use these
  symbols until it is acceptable to all or the new symbols are backed out.

  This symbol rename will have the unique quality that
  strlen("API_EXPORT") == strlen("AP_DECLARE"), therefore the mass symbol
  rename will not throw off function continuation lines.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86539 13f79535-47bb-0310-9956-ffa450edef68