The new behavior is that it will flush when either the pending batch has grown
to the specified size, or the time interval has expired.

For some reason there wasn't an entry in indra/llcommon/CMakeLists.txt to run
the tests in indra/llcommon/tests/lleventfilter_test.cpp. It seems likely that
at some point it existed, since all previous tests built and ran successfully.
In any case, (re-)add lleventfilter_test.cpp to the set of llcommon tests.
Also alphabetize them to make it easier to find a particular test invocation.

Also add new tests for LLEventThrottle.

To support this, refactor the concrete LLEventThrottle class into
LLEventThrottleBase containing all the tricky logic, with pure virtual
methods for access to LLTimer and LLEventTimeout, and an LLEventThrottle
subclass containing the LLTimer and LLEventTimeout instances and corresponding
implementations of the new pure virtual methods.

That permits us to introduce TestEventThrottle, an alternate subclass with
dummy implementations of the methods related to LLTimer and LLEventTimeout. In
particular, we can explicitly advance simulated realtime to simulate
particular LLTimer and LLEventTimeout behaviors.

Finally, introduce Concat, a test LLEventPump listener class whose function is
to concatenate received string event data into a composite string so we can
readily test for particular sequences of events.

plus LLEventBatch::getSize(), setSize()
plus LLEventThrottle::getPostCount() and getDelay().

The interesting thing about LLEventThrottle::setInterval() and
LLEventBatch::setSize() is that either might cause an immediate flush().

These classes are as yet untested: they are straw people for API review, based
on email conversations with Caladbolg and Rider.

MAINT-6336: Centralize waiting on event pump with a timeout. Shorten the lifespan of a timeout event pump lifespan to be no longer than necessary. Change all references to the LLEventTimer to instead uses the centralized version.

svn merge -r113003:119136 svn+ssh://svn.lindenlab.com/svn/linden/branches/login-api/login-api-2 svn+ssh://svn.lindenlab.com/svn/linden/branches/login-api/login-api-3