Also add a test.

This is the last of the openssl/asn1.h includes from the directories that are
to be kept in the core libcrypto library. (What remains is to finish sorting
out the crypto/obj stuff. We'll also want to retain a decoupled version of the
PKCS#12 stuff.)

Functions that need to be audited for reuse:
i2d_DHparams

BUG=54

Change-Id: Ibef030a98d3a93ae26e8e56869f14858ec75601b
Reviewed-on: https://boringssl-review.googlesource.com/7900
Reviewed-by: Steven Valdez <svaldez@google.com>
Reviewed-by: David Benjamin <davidben@google.com>

Initial fork from f2d678e6e8 (1.0.2 beta).

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