2010-09-01 : fixed a bug on mac 32bit when reading in net3 version string

2010-09-01 : some vars with grid and singleton dims were wrongly analyzed by cmor_variable has not being defined with the right number of dimmensions.
2010-09-01 : updated doc. Was saying you can pass "none" for units when it really is: ""
2010-09-01 : updated doc. Was wrongly stating you can pass "none" if no missing_value