Fix portability issues with the Capsicum patch committed in r339216:

• Wrap access to pw_change and pw_expire in the appropriate #ifdefs.
• Wrap calls to login_cap(3) API in appropriate #ifdefs.
• Add wrapper for transferring time_t, which is still only 32 bits wide on FreeBSD i386.
• Use a temporary variable to deserialize size_t.

Approved by: re (gjb)