Update OS_NS_dlfcn.inl

fixed  ACE_OS::dlsym function that it works for VxWorks - older than 6.9.
Update OS_NS_dlfcn.inl

changed how is it checked for VxWorks version (using: (ACE_VXWORKS < 0x690)).
Update config-vxworks6.4.h

lack of rand_r and wstring is tru also for older version of VxWork, so we can move:
# define ACE_LACKS_RAND_R 1
# define ACE_LACKS_STD_WSTRING
from config-vxworks6.8.h to config-vxworks6.4.h
Update config-vxworks6.8.h

# define ACE_LACKS_RAND_R 1
# define ACE_LACKS_STD_WSTRING
should be move to (they have been moved)
to: config-vxworks6.4.h
Merge pull request #1 from bjeram/master

Broken dlsym for older version of VxWorks