Fixed two fd leaks in mhparse.c.

Fixed two fd leaks in mhparse.c.
1) In openQuoted(), the decoded contents file was opened twice in
   succession. The second open was added by a patch in March 2000.
2) openBase64(), openQuoted(), and open7Bit() could open the contents
   file, but it never would be closed. Added code to each to close the
   file if the function opened it.
[Bug #24004: (debbug 344182)]

Pulled in from nmh. Thanks to David Levine.