Stop using a deprecated (as of OS X 10.9) function to get OS X version.

CFURLCreateDataAndPropertiesFromResource() is not listed as being deprecated.
It still works but this code goes to a lot of effor to use OS X's
CoreFoundation framework to read the plist when we have our own functions
for reading files.  I think it's much better for our maintenance purposes to
use our functions for as much as we can.

* subversion/libsvn_subr/sysinfo.c
  (write_to_cfmutabledata): svn_write_fn_t implementation that feeds data into
    a CFMutableDataRef (Core Foundation's version of streams).

  (system_version_plist): Use our stream interface to read the plist files
    and wire it up to a stream that feeds the data to a CFMutableDataRef
    so we can still let OS X's property list code do the parsing for us.
    Also fix a small comment typo.


git-svn-id: https://svn.apache.org/repos/asf/subversion/trunk@1573096 13f79535-47bb-0310-9956-ffa450edef68