Add additional KRB5_TRACE points

Add additional KRB5_TRACE points

Add additional tracing points to the PKINIT plugin for use with the
KRB5_TRACE facility, replacing many (but not all) of the existing
pkiDebug() trace points.

Fix a memory leak of an errinfo structure when loading a PKCS11 module
fails.

Rename pkinit_pkcs11_code_to_text() to pkcs11err() for brevity, and
modify it for thread safety.

[ghudson@mit.edu: added certificate index to regexp match trace
points; renamed various identifiers; edited commit message]

ticket: 8999 (new)