Bug in gsl_integration_qawc and correction

[Axel Hutt]

Dear all,

there is a bug in the quadrature routine for Cauchy principal
values in gsl_integration_qawc. 

The problem is, that for a special relation of integration interval 
(a,b) and singularity, the bisection routine in 
$(GSL-ROOT-DIR)/integration/qawc.c might lead to integration borders 
a1=c or b1=c, which yields NaN from qc25c(..) for the integral.
This is easily resolved by changing the check in which subinterval
c lies (line 133) from

if (c > a1 && c < b1)

to 

if (c >= a1 && c <= b1)

(or equivalently for a2 and b2 in line 138), just add equation signs 
in qawc.c in line 133.

Unfortunately, I do not know how to handle patch files, sorry for
this.

Axel