improve output of ecmfactor
When we run ecmfactor, it prints the curves used:
./ecmfactor -t 8 11111111111111111111111111111111111111111111111 1e3
Performing 8 curve(s) with B1=1000
thread 0 with sigma -1:1837057832 found no factor
thread 1 with sigma -1:3255926922 found no factor
thread 2 with sigma -1:3074399962 found factor in step 2: 35121409
thread 3 with sigma -1:4279826370 found no factor
thread 4 with sigma -1:3877204156 found no factor
thread 5 with sigma -1:3553938543 found factor in step 1: 35121409
thread 6 with sigma -1:3476095635 found factor in step 1: 35121409
thread 7 with sigma -1:1758733336 found no factor
where sigma -1:nnn means a default curve. It would be better if -1 was replaced with the real type of curve used (0, 1, 2, 3).