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.

crypto/rand/rand_egd.c

@@ -114,7 +114,7 @@ int RAND_egd_bytes(const char *path,int bytes)
 #include <sys/types.h>
 #include <sys/socket.h>
 #ifndef NO_SYS_UN_H
-# ifdef OPENSSL_SYS_VSWORKS
+# ifdef OPENSSL_SYS_VXWORKS
 #   include <streams/un.h>
 # else
 #   include <sys/un.h>