In order to minimise the upstream diffs needed for bits of Android to
build with BoringSSL, this change implements the old style PKCS#12
functions as wrappers around the modern parser.

The function to read all the contents of a BIO could almost be a utility
function but I'll wait until there are two uses for it first.

The important change from the original functions is that these will
always read the complete buffer/BIO/FILE passed in. Based on a survey of
uses of d2i_PKCS12 that I found, this appears to be universally what
callers want anyway.

Change-Id: I3f5b84e710b161d975f91f4d16c83d44371368d1
Reviewed-on: https://boringssl-review.googlesource.com/1791
Reviewed-by: Adam Langley <agl@google.com>

This is cleaner than the OpenSSL code was, at least, but it's hardly
beautiful due to the "standard" that it's trying to implement. (See
[1].)

The references from the PKCS#8 code to various ciphers have digests have
been made into function pointer references rather than NIDs so that the
linker will be able to drop RC2 code for binaries that don't call PKCS#8
or #12 functions.

A bug that crashed OpenSSL/BoringSSL when parsing a malformed PKCS#8
structure has been fixed too.

See https://www.cs.auckland.ac.nz/~pgut001/pubs/pfx.html

Change-Id: Iaa1039e04ed7877b90792835e8ce3ebc3b29f89e
Reviewed-on: https://boringssl-review.googlesource.com/1592
Reviewed-by: Adam Langley <agl@google.com>

Initial fork from f2d678e6e8 (1.0.2 beta).

(This change contains substantial changes from the original and
effectively starts a new history.)