In PKINIT, use library initializer for OpenSSL

Use a library initializer to prevent multiple threads using PKINIT
from concurently initializing OpenSSL functions.  For cases where
MT-safety is not assured by registering OpenSSL locking callbacks,
this significantly lowers the odds of crashes caused by races in
OpenSSL initialization.  (If OpenSSL initialization functions are
called by some other thread directly, crashes are still possible.)

[ghudson@mit.edu: simplify code changes and commit message]

ticket: 6413