Update info interface

[bruceravel]

No description provided.

[joddie]

There are some minor changes in commit db98e06 that fix some (most?) problems with the info-look setup, so completion and symbol lookup work properly with the info file from gnuplot v4.4. Hopefully it will still do the right thing with older versions, by keeping the old setup when gnuplot version is < 4.0.

Unrelated, but it should be pretty easy to change things to use the symbol completion functions provided by comint, which would give us a standard completion-mode popup buffer when there are alternatives. I'll try to do this in the next couple of days.