This is harder than with OpenSSL, since OpenSSL counts the bytes on
its own and NSS doesn't. To fix this, we need to define a new
PRFileDesc layer that has its own byte-counting support.
Closes ticket 27289.
Also, add a stubbed-out nss version of the modules. The tests won't
pass with NSS yet since the NSS modules don't do anything.
This is a good patch to read with --color-moved.
I am calling the crypto library "crypt_ops", since I want
higher-level crypto things to be separated from lower-level ones.
This library will hold only the low-level ones, once we have it
refactored.
Nick Mathewson