Wrong units for REL_HUMID in comments of vicNl_def.h

[tbohn]

in vicNl_def.h, REL_HUMID and OUT_REL_HUMID are described in comments as having units of [fraction]. But in initialize_atmos(), REL_HUMID is actually assumed to be a percent, and is divided by 100. So users looking at vicNl_def.h will be misled.

All that needs to happen is to correct the comments. I'd be happy to do this as part of hotfix 4.1.2.i.