Make the number of context lines in the diff output handing dynamic
instead of static. This prepares the code for making it configurable
as part of revving the calling functions (which is necessary anyway
for adding cancellation support).

* subversion/libsvn_diff/diff_file.c
  (includes): Add assert.h.
  (svn_diff__file_output_baton_t): Add context_size.
  (output_unified_flush_hunk,
   output_unified_diff_modified): Update user.

  (svn_diff_file_output_unified4): Initialize baton.
  (context_saver_t): Make context size dynamic.
  (context_saver_stream_write): Update user.
  (svn_diff3__file_output_baton_t): Add context_size.
  (flush_context_saver): Update caller.
  (make_context_saver): Update initialization.
  (trailing_context_printer): Update comment.
  (make_trailing_context_printer): Update initialization.
  (output_conflict_with_context): Update user.
  (svn_diff_file_output_merge2): Update initialization.

* subversion/libsvn_diff/diff_memory.c
  (unified_output_baton_t): Add context_size.
  (output_unified_flush_hunk,
   output_unified_diff_modified): Update user.

  (svn_diff_mem_string_output_unified2): Update initialization

  (context_saver_t): Update variables.
  (context_saver_stream_write): Update user.
  (merge_output_baton_t): Add context_size.
  (flush_context_saver): Update user.
  (make_context_saver): Properly initialize baton.
  (trailing_context_printer): Update comment.
  (make_trailing_context_printer,
   output_conflict_with_context): Update user.
  (svn_diff_mem_string_output_merge2): Update initialization.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1597976 13f79535-47bb-0310-9956-ffa450edef68