MA86 Z headers not working with C++

[cnpetra]

MA86 Z headers are not working with C++ when std::complex includes are present.

A temporary dirty-ish fix below.

1. In the MA86 'include' directory, copy 'hsl_mc69z.h" and "hsl_ma86z.h" to 'hsl_mc69z.hpp" and "hsl_ma86z.hpp"

Edit 'hsl_mc69z.hpp" and "hsl_ma86z.hpp" as in 2, 3, and 4 below.

2. After #include <complex.h> add these lines

#ifdef __cplusplus
extern "C" {
#endif

3. replace "complex" with "_Complex" whenever occurs in "double complex" or "complex double"

4. before the last #endif insert these lines

#ifdef __cplusplus
}
#endif

[cnpetra]

became obsolete in some sense. umfpack is used now instead as it turned out that the Kron reduction needs to factorizations of nonsymmetric matrices.