Use Throwable.getMessage() when logging exceptions.

Use Throwable.getMessage() when logging exceptions.

The VM's internal exception logger was pulling the exception's detail
message out of a field in Throwable.  This gets the wrong answer when
the exception overrides getMessage().

The VM now invokes the appropriate getMessage() method and displays
that instead.  This is of particular interest in CheckJNI failure
messages.

Also, don't assert that switching from "running" to "running" is
a problem.  It's a bit weird, but there's nothing wrong with it,
and there's a fair chance that the updated exception log function
will do it.

Bug 2845581

Change-Id: Id8d77221129ae7b45473e700a79a335164049362