Add new error message wrapping APIs

This commit adds krb5_[v]prepend_error_message[2]() public functions for
wrapping error messages.  They are public so that, for example, plugins
can use them.

Conflicts:
	src/lib/krb5_32.def
Use new error message wrapping APIs

Conflicts:
	src/lib/kdb/kdb5.c
	src/lib/krb5/krb/fast.c
	src/lib/krb5/krb/get_in_tkt.c
	src/lib/krb5/krb/preauth2.c
	src/plugins/kdb/ldap/libkdb_ldap/kdb_ldap.c
	src/plugins/kdb/ldap/libkdb_ldap/kdb_ldap_conn.c
Add [libdefaults] err_fmt parameter

Conflicts:
	src/include/k5-int.h
Include file ccache name in error messages

Conflicts:
	src/lib/krb5/ccache/cc_file.c
Test err_fmt