Bring over changes from source of truth in pkgsrc - bump version to 20200503

Update netpgpverify and libnetpgpverify to version 20200503

ensure all exported functions use a unique prfix, so that

Bring over changes from source of truth in pkgsrc - bump version to 20200503

Update netpgpverify and libnetpgpverify to version 20200503

ensure all exported functions use a unique prfix, so that they don't
conflict with symbols (both data and text) in libcrypto. this works for
statically linked binaries and libraries, rather then the version map which
only works for dynalically-linked.

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Sync with pkgsrc sources as of version 20160614

+ pick up renaming changes to internal routines
+ fix for issue verifying signatures created by gpg --no-emit-version
+ add test for same

Update the bignum implementation in netpgpverify, and sync all uses of it

+ radix conversion routines added
+ bitwise operations added
+ whitespace cleanups

Bring over the standalone netpgpverify sources from
pkgsrc/security/netpgpverify.

No functional change.