Merge r960671 from trunk:

Only deal with the mutex when XTHREAD is enabled. This increases the
performance of buffered reads/writes tremendously.

* file_io/win32/readwrite.c:
  (apr_file_read, apr_file_write): only manipulate mutex when XTHREAD

Submitted by: Ivan Zhakov <ivan visualsvn.com>


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/branches/1.5.x@1534139 13f79535-47bb-0310-9956-ffa450edef68