Add leading underscore to data symbols.

ChangeLog

ecc-192.c

ecc-224.c

ecc-256.c

ecc-384.c

ecc-521.c

ecc-curve.h

examples/ecc-benchmark.c

examples/hogweed-benchmark.c

nettle-lookup-hash.c

nettle-meta-aeads.c

nettle-meta-armors.c

nettle-meta-ciphers.c

nettle-meta-hashes.c

nettle-meta.h

testsuite/ecc-mod-test.c

testsuite/ecdh-test.c

testsuite/ecdsa-sign-test.c

testsuite/ecdsa-verify-test.c

testsuite/testutils.c