[PATCH] fix libsvn_auth_gnome_keyring.pc w/libsecret

libsvn_auth_gnome_keyring.pc is wrong in 1.10.0; when built against
libsecret it still references the gnome-keyring library.

...
Requires: apr-1 gnome-keyring-1
Requires.private: libsvn_subr

The dep should also be private; fix attached OK?

[[[
Fixes libsvn_auth_gnome_keyring.pc when configured with libsecret, and
make dependencies private.

* configure.in, build/ac-macros/libsecret.m4:
  Set SVN_GNOME_KEYRING_PCLIBS to libsecret/gnome-keyring as appropriate.

* build.conf (gnome-keyring):
  Substitute SVN_GNOME_KEYRING_PCLIBS as private deps of
  libsvn_auth_gnome_keyring in generated pkg-config file.
]]]