Data-driven ASN.1 decoder

Data-driven ASN.1 decoder

Add a general ASN.1 decoder implementation in asn1_encode.c using the
same data structures as the encoder (augmented where necessary), and
use it to define decoder functions in asn1_k_encode.c.  Add a boolean
type to atype_info, as it is needed for the pa_pac_req decoder.  For
the moment, just #if out the old decoder functions; they and their
support code can be cleaned up later after a a few remaining utility
functions are addressed.

Changes to encoder and decoder interfaces are minimized, but there are
two small ones.  ldap_seqof_key_data has a kvno field added, and some
of the decoder logic is pushed up into the caller.  The safe_with_body
decoder now outputs an allocated krb5_data * instead of a krb5_data
with aliases into the input buffer.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@25693 dc483132-0cff-0310-8789-dd5450dbe970