Map race fixed. TLS client support. LogClient improvements

Servers

A race condition was fixed that affected sparse Merkle trees as served by the map server.

Utilities / Binaries

The maphammer uses a consistent empty check, fixing spurious failures in some tests.

The createtree etc. set of utilities now support TLS via the -tls-cert-file flag. This support is also available as a client module.

Log Client

GetAndVerifyInclusionAtIndex no longer updates the clients root on every access as this was an unexpected side effect. Clients now have explicit control of when the root is updated by calling UpdateRoot.

A root parameter is now required when log clients are constructed.

Other

The Travis build script has been updated for newer versions of MySQL (5.7 through MySQL 8) and will no longer work with 5.6.