text buffer newline fix

[Havoc Pennington <hp redhat com>]

Hi,

I made an attempt to fix the issue where text buffers always contained
a newline. You can now have zero-length buffers, and set_text/get_text
pairs behave as expected.

I think this will make everyone happy in the end, but for now stuff is
probably broken. Please file bugzilla reports as you discover said
stuff...

Havoc