ITSOL build system integration

[c.]

Nir, 

FYI yesterday I helped Kai integrate ITSOL in Octave's build system [1].
Now Octave will check automatically for ITSOL headers and libraries 
when being configured. 

Kai, one thing we forgot to do is to change all ITSOL dependent .cc files
so that they can error out gracefully if ITSOL is not installed on the system.

This should be done by wrapping all the code in a preprocessor conditional like

#ifdef HAVE_ITSOL

…

#else

error ("iluk: this version of Octave has been built without ITSOL, therefore 
this functionality is not available.")

#endif

HTH,
c.

[1] http://inversethought.com/hg/octave-kai/rev/b34ec4b2064b