ENH: option to raise an error when get_subjects_dir() finds nothing
FIX: add subjects_dir parameter to do_forward_solution()
MISC/COSMITS: addresses minor doc and viz style issues

- fix doc string for equalize epochs count method
- red instead of black hline for evoked plots (now that the default to black
black hlines are not easy to discern.). I prefer this to adding another compicated dict as param.
ENH : add qrs thresh in options of mne_compute_proj_ecg.py
Merge pull request #484 from dengemann/fix_whitened_evoked

MISC/COSMITS: addresses minor doc and viz style issues
Merge pull request #477 from christianmbrodbeck/fix-test

FIX TEST test_forward: change subjects_dir
Merge pull request #485 from agramfort/qrsthr

ENH : add qrs thresh in options of mne_compute_proj_ecg.py