[9fans] frames & tabs

[Fco.J.Ballesteros <nemo@gsyc.escet.urjc.es>]

Since tabs are meant to tabulate and I think that means
keeping clear columns, I was thinking about a change for libframe
to handle tabs like follows:

1. Keep an array of tab positions per frame, each one pointing to the x
where the respective column should start.

2. Adjust each tab position as text gets inserted.


So that if you insert:
	a\tb\tc\n
You get
	a b c
And when later  you insert:
	ab\tcde\n
You get
	a  b   c
	ab cde

The first bad thing is that text before the insertion gets `changed'
by inserting tabs in the following lines.

The second bad thing is that tabs on the left of the line (eg. source code)
would still be handled by inserting N spaces.

Does it all make sense?