cglumin: calculate luminosity

A convolution model to calculate the luminosity of other model components, for galactic sources. For example:

   cglumin*phabs*(pow + gauss)

with the normalization of the power-law model fixed to a non-zero value gives the luminosity and error on the entire model.

   phabs*cglumin*(pow + gauss)

again with the normalization of the power-law fixed to a non-zero value gives the unabsorbed luminosity and error. Finally,

   phabs*(pow + cglumin*gauss)

with the normalizaton of the gaussian fixed to a non-zero value gives the luminosity and error on the gaussian component. Note that when the cglumin model is used the normalization of one of the additive models must be fixed to a non-zero value. It is also important to ensure that the energy range over which the model is calculated (which is determined by the response matrix in use) covers the energy range for which the luminosity is calculated. If the model to which the cglumin is applied integrates to zero then a divide-by-zero error will occur resulting in NaN values for the fit statistic.

Parameters are:

par1=Emin	Minimum source frame energy over which luminosity is calculated.
par2=Emax	Maximum source frame energy over which luminosity is calculated.
par3=Distance	Distance to the source in units of kpc.
par4=lg10Lum	log (base 10) luminosity in units of erg/s.