Enable DSO loading and "prelinked" support for RA libraries.
Enable DSO loading and "prelinked" support for RA libraries.

(ra_libraries[]): new data structure to define RA library names and, if
  linked-in, their initialization function

(load_ra_module): new function to load an RA module if DSO support is
  available, and the module can be found.

(svn_client_init_ra_libs): revamp to use ra_libraries. linked-in functions
  are preferred; otherwise, we try to load the RA module.
  rename "url_type" to "url_scheme"

(svn_client_get_ra_library): update scheme comparison logic -- schemes are
  case-sensitive and must be followed by a colon.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@838624 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,wbond/subversion,wbond/subversion,wbond/subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,wbond/subversion,YueLinHo/Subversion,YueLinHo/Subversion