Configure missing a step

[Scott Ritchie]

I managed to get past configure and then have a compile error due to a
missing header file: intrinsic.h

Configure should be checking for this file, like it checks for flex and
bison and such.  The package I needed to install was libxt-dev

I'm on Ubuntu at the moment, but this should be true for all Debian
systems.

Could someone else clean this up?  I'm scared to touch configure.

-Scott Ritchie