support -pylab flag with deprecation warning

[minrk]

As requested on the list, the -pylab flag (one -) is allowed once again. If present, the argument is transformed to the current syntax, and a warning is displayed.

[minrk]

Pinging @fperez and @bgranger. This specifically supports -pylab only. Flags still require -- prefix. An alternative would be to accept single-- prefix for all flags. This would be more natural for flags like ipython -i for force-interactive. Leaving it as-is gives us a place to add something new in the future.

[fperez]

My take on this is to be conservative for now. -pylab is special because it's extremely widely documented, so we don't really want everyone's scripts, aliases and habits to break everywhere. We'll have to fine-tune our handling of command-line args after more extensive field use and feedback, so I'd suggest we stick, for now, to the bare minimum of tweaks until we can collect such information post-0.11.

[minrk]

That makes sense. I'll go ahead and merge when I am back at a computer this evening.

[ellisonbg]

I am +1 on having this. I also like that this logic only applies to -pylab and not all flags/options.