Refuse RSA keys <1024 bits in length. Improve reporting
for keys that do not meet this requirement. ok markus@
Upstream-ID: b385e2a7b13b1484792ee681daaf79e1e203df6c
[bufaux.c bufbn.c bufec.c buffer.c buffer.h sshbuf-getput-basic.c]
[sshbuf-getput-crypto.c sshbuf-misc.c sshbuf.c sshbuf.h ssherr.c]
[ssherr.h]
New buffer API; the first installment of the conversion/replacement
of OpenSSH's internals to make them usable as a standalone library.
This includes a set of wrappers to make it compatible with the
existing buffer API so replacement can occur incrementally.
With and ok markus@
Thanks also to Ben Hawkes, David Tomaschik, Ivan Fratric, Matthew
Dempsky and Ron Bowes for a detailed review.