deleted bug when all simulated sources are located in only one hemisphere
WIP: complete drop log
COSMITS
ENH: add tests, fix bug
ENH/STY: simplify drop_log add on
Merge pull request #594 from dengemann/improve_droplog

ENH: Improve epochs drop_log
Merge pull request #583 from joewalter/bug_in_simulator

deleted bug when all simulated sources are located in only one hemisphere