Session sometimes partially restored

[dbarnett]

What steps will reproduce the problem?

1. Launch a8 with session saving enabled, and open a lot of files for editing.
2. Exit a8.
3. Re-launch a8.

What is the expected output? What do you see instead?
I expect to see all the same buffers open in the same configuration as before I closed a8. Instead, I sometimes see several buffers missing, sometimes also with syntax errors from vim that suggest it's getting an unexpected EOF.

It may help reproduce if you have a complex configuration with tabs and splits, and might also help reproduce if you have plugins installed that add a noticeable delay after opening each buffer.

[dbarnett]

I suspect what's happening here is that we're calling the periodic ":mksession" command before vim finishes processing the session the first time, and clobber the session file it's reading.