corrected a constant that was set for the ATMega in pulseIn.  pulseIn should now be quite accurate down to 2us. (cherry picked from commit 192cb828bd8b2e88b207cf59bc462e601aecf189)
corrected a constant that was set for the ATMega in pulseIn.  pulseIn should now be quite accurate down to 2us.
(cherry picked from commit 192cb828bd8b2e88b207cf59bc462e601aecf189)

jaehong/Xmegaduino,jaehong/Xmegaduino,jaehong/Xmegaduino,jaehong/Xmegaduino,jaehong/Xmegaduino,jaehong/Xmegaduino,jaehong/Xmegaduino