Only _WIN32 is defined by the compiler, and WIN32 is not standardized
and may be missing.

Closes #169

Use milliseconds precision to reduce rounding errors.

Move from db/DatabaseGlue.cxx, eliminating global variable.

Call GetDatabase() only once.

The proxy plugin has now implemented the "idle" event listener.

Ask the DatabasePlugin for stats when the first client requests them,
not at startup.

Reduce GLib usage.

Don't use GTimer if the operating system is able to tell us the
uptime.

Refactor SimpleDatabase::GetLastModified() to be generic for all
plugins.  Remove the SimpleDatabase assumption from db_stats_print(),
allowing it to be implemented by all database plugins.

Fixes crash on "stats" in certain configurations.

Eliminate redundant declaration.

Unused outside of Stats.cxx.

Publish the Client API, preparing to move more code into the Client
class.

Use forward declaration instead.