Revision 1500762

Prevent the GPG Agent password store from overriding other password stores
even though no usable GPG Agent is running.

* subversion/libsvn_subr/gpg_agent.c
  (find_running_gpg_agent): New helper function that finds a running GPG Agent.
   This code was split out from the upper half of ...
  (password_get_gpg_agent): ... this function.
  (password_set_gpg_agent): Don't unconditionally set *done to TRUE. While it
   is correct that we don't need to explicitly store the password in the agent,
   this function must check whether a usable GPG Agent exists. Otherwise,
   users might be left with no usable password store, since the gpg-agent
   store wrongly claims that the password was saved, when it actually wasn't.