Following up on r1597983 and r1618839, expose configurable context size via
the now revved svn_diff_mem_string_output_unified3() function.

* subversion/include/private/svn_diff_private.h
  (svn_diff__display_prop_diffs): Add context_size argument.

* subversion/include/svn_diff.h
  (svn_diff_mem_string_output_unified3): Add context_size.
  (svn_diff_mem_string_output_unified2): Tweak documentation.

* subversion/libsvn_client/diff.c
  (display_prop_diffs): Update caller.

* subversion/libsvn_diff/deprecated.c
  (svn_diff_mem_string_output_unified2): Update caller.

* subversion/libsvn_diff/diff_memory.c
  (svn_diff_mem_string_output_unified3): Add argument.

* subversion/libsvn_diff/util.c
  (svn_diff__display_prop_diffs): Add argument.

* subversion/svnlook/svnlook.c
  (display_prop_diffs): Update caller.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1618844 13f79535-47bb-0310-9956-ffa450edef68