A little spring-cleaning

In order not to introduce too many new files for the ILU preconditioners in libinterp/dldfcn I made heavy use of C++ templates and merged real and complex versions into one file. This decision has been supported by the fact, that nearly all steps for real and complex input are the same, just function names and data types have to be changed accordingly. I hope not to be the only one agreeing on this trade-off between code duplication and clarity :-/

The integration of ITSOL and ZITSOL into GNU/Octave so far can be summarized as follows:

	ITSOL	ZITSOL
ILUK*	yes	yes
ILUT	yes	yes
ILUC*	yes	experimental**
ILUTP*	no	no

* Function is important for the MATLAB compatibility wrapper ilu.m
** Own complex implementation analogous to real version

The current interface can be obtained from this archive (does not require a development version of GNU/Octave) or from my repository.