On the svn-auth-x509 branch: Change the UTF conversion functions to accept
and return counted strings that contain NUL values.

* subversion/include/private/svn_utf_private.h
  (svn_utf__encode_ucs4_string): Update docstring.
  (svn_utf__utf16_to_utf8): Return a counted string and require the length
   of the source string; and update docs accordingly.
  ((svn_utf__utf32_to_utf8): Likewise.

* subversion/libsvn_subr/utf.c
  (svn_utf__utf16_to_utf8, svn_utf__utf32_to_utf8): update to match
   the changed prototype and semantics.

* subversion/tests/libsvn_subr/utf-test.c
  (test_utf_conversions): Update tests to match new function semantics.
   Add tests for counted strings containing NUL bytes.


git-svn-id: https://svn.apache.org/repos/asf/subversion/branches/svn-auth-x509@1613604 13f79535-47bb-0310-9956-ffa450edef68