Remove svn_client_ctx_t from svn_client_conflict_t

Hi Stefan,

Currently svn_client_conflict_t stores a pointer to svn_client_ctx_t
inside and uses it for every operation like
svn_client_conflict_tree_get_details() or
svn_client_conflict_*_resolve(). It may be useful for simple cases,
but for other cases it makes using new API more difficult. That's
because an API user needs to guarantee that lifetime of
svn_client_ctx_t is longer than of the svn_client_conflict_t instance.

I suggest changing svn_client_conflict_* API so that it wouldn't keep
reference to svn_client_ctx_t and add it as argument to all API
functions where it's required.

I can do that, if there are no objections. What do you think?

-- 
Ivan Zhakov