A real breakpoint makes entries in the breakpoint filter for all offsets at the given line. Various flow control commands will also use the breakpoint filter to add and remove temporary "internal breakpoints" required during the flow operation. Ensure that we never remove a breakpoint filter entry if there was already one there due to a breakpoint (or really any other reason).
Small stepping, which is stepping over sub-expressions (kinda), worked but was a little goofy. The mode was set on the client, passed over with control flow commands, placed on the execution context, then retrieved from there and used by those same flow commands. Removed the execution context part of it, since it was useless, and factored grabbing the offsets into the flow cmds where they belong instead of doing it all the time.
The run cmd also had some notion of small stepping, but you'll note it was never sent over the wire. Nuked that, since it never mattered anyway.
Add reasonable behavior for stepping within continuations (generators). Stepping over a yield now does what one would expect. When the generator is driven from a C++ extension like ASIO, the next logical execution point is after the yield statement, and that's where we'll stop now. When driven from PHP, say in a loop calling send(), the next execution point is in fact the call site of send(), so we go there. Stepping off the end of the generator function, goes to the caller of send(), or the caller of the C++ extension. Stepping _out_ of a generator driven by a C++ extension ensures that we go to the caller and not back into the generator again. The logic for both cases is exactly the same. The difference comes from the fact that we don't actually debug C++ extensions.
This also fixes a long-standing problem where breakpoints would interfere with control flow cmds on the same source line. This caused funny behavior, like taking multiple steps to get off of a breakpoint.
Mike Magruder