core: Make use of --homedir in gpgconf.
* src/engine-gpgconf.c (struct engine_gpgconf): Add field 'version'. (have_gpgconf_version): New. (gpgconf_release): Free VERSION. (gpgconf_new): Set VERSION. (gpgconf_read, gpgconf_write): Use --homedir with recent gnupg.
- Signed-off-by: Werner Koch <wk@gnupg.org>