cexp() function API has changed in C99

[Alex Valavanis]

Major issue found by Paul Harrison:

The old definition of the complex exponential in his old maths.h header was:

cexp(x):

   \exp(i \times x)

where x is a REAL number (G.r, in this case), while the C99 standard
defines it as:

cexp(z):

  \exp(z)

where z is a COMPLEX number.

Since we migrated to the new complex data type, this has broken the calculations in ppcd/ppsl and pplbso.

The solution is to change our function calls from:

cexp(x)

to

cexp(I*x)

Note though, that this will in turn be removed when we switch to using the std::complex<double> data type when the programs migrate to C++.

[Alex Valavanis (valavanisalex)]

Backported to lp:qwwad/1.2.x r338