Add a few more VxWorks targets.

Correct misspelled VXWORKS macros.
Add VXWORKS identifying macros to e_os2.h.
Add required inclusions and mappings for VxWorks in e_os.h.
A few small modifications to make OpenSSL build and work on VxWorks.
PR: 253, except for the  change that was handled in an earlier
         commit, and a request for easy build of just parts of OpenSSL.