Fix incr seq timing in get multi

[blackmad]

we are calling incrSeq after constructing the getMulti request when we should be incrementing it before.

here's what currently happens

• seq = N
• getMulti() is called
• runs a bunch of fast local logic/loops to break up the keys into per-server batches
• per server, we start sending out requests to the first server with seq=N, the second server with seq=N+1, etc etc

what I think is happening is

• seq = N
• getMulti() is called
• batch N+B does a bunch of work building request frames
• in the middle of one of those, a getVersion() call is made
• it increments seq to N+B+1,
• original getMulti call keeps working through the same batch but now with N+B+1 (since it didn't save seq at the start of the loop, and keep it until the end), so now we overwrite the N+B+1 handler (that was the getVersion handler) with the getMulti handler, which is now going to get an unexpected getVersion response

solution: save the current seqno for the entire getMulti run