ra_svn: clarify the protocol documentation.
ra_svn: clarify the protocol documentation.

* subversion/libsvn_ra_svn/protocol
  (Syntactic structure): Remove mention of braces from alternative choices.
  (propdelta, lock-many): Correct spacing in prototypes.
  (Extensibility): Rewrite, removing references to braces and the (incorrect)
    assertion that all new parameters must be in a tuple, and adding an example
    of a mandatory parameter.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@863969 13f79535-47bb-0310-9956-ffa450edef68

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