Fix building with libtasn1 < 3.1

The data type ASN1_ARRAY_TYPE is deprecated, but still available
in current versions of libtasn1.

This fixes building with the version of libtasn1 from current
debian stable.
Merge pull request #3 from mstorsjo/old-libtasn1

Fix building with libtasn1 < 3.1