If I comment out the /etc/fstab entry for the USB hard drive it will boot without the mouse/keyboard but then I can't mount the USB hard drive as /dev/sda1 doesn't exist after it boots, even if I unplug and replug the USB drive (not really an option). While I may not have permuted all the sequence possibilities, /dev/sda & /dev/sda1 only seem to exist if I boot with a mouse/keyboard attached or attach a mouse/keyboard and then login from the console.
After some more trial and error this is even weirder.
I had my mouse/keyboard on a USB (powered) hub along with a web cam and BT dongle. So I started trying other things, directly into the Pi USB along with the USB drive to see what was required for the bootup with the USB drive to succeed. Wireless 2.4GHz mouse/keyboard prevents bootup same as having not having the hub (with the mouse/keyboard) plugged in. So I tried a USB to PS/2 mouse/keyboard adapter, still nogo with all three possibilities -- nothing, PS/2 keyboard only, PS/2 mouse+ keyboard (the PS/2 keyboard works in emergency mode. Then I tried just a USB mouse, nogo, then I tried my USB mouse and keyboard (removed from the disconnected hub) and still nogo!
This is just too strange. I then tried the USB hub with everything unplugged and it booted fine! Then I tried with the hub unpowered and nogo. I had an older cheaper hub lying around and tried it powered and unpowered, nogo.
This just makes absolutely no sense to me!
This hub setup is normally my "test jig" with Logitech mouse (trackball actually) and Logitech USB keyboard along with a couple of web cams and a BT dongle. This way I can easily switch between the RPi2 and Beaglebone Black (which needs a powered hub for most anything).
The hub that doesn't work shows:
ID 05e3:0608 Genesys Logic, Inc. USB-2.0 4-Port HUB
with lsusb when plugged into another system.
On the RPi2 booted with the USB drive and empty powered hub lsusb shows:
Bus 001 Device 005: ID 0bc2:ab28 Seagate RSS LLC
Bus 001 Device 006: ID 1a40:0101 Terminus Technology Inc. 4-Port HUB
Bus 001 Device 004: ID 1a40:0101 Terminus Technology Inc. 4-Port HUB
Bus 001 Device 003: ID 0424:ec00 Standard Microsystems Corp. SMSC9512/9514 Fast Ethernet Adapter
Bus 001 Device 002: ID 0424:9514 Standard Microsystems Corp.
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
I believe the pair of Terminus Technology 4-port hubs are the "generic" 7-port hub I'm using.
It would suck, but I may have to go back the Wheezy as in its intended use and location I can't have a bunch of crap hanging off it and plugging in another wall wart for the hub is problematic.