start_date broke commit_begin command line option

[janihur]

I think commit 780c0fd (start_date command line option) introduced a bug that broke commit_begin command line option.

def getlogrange(defaultrange = 'HEAD', end_only = True):
    commit_range = getcommitrange(defaultrange, end_only)
    if len(conf['start_date']) > 0:
        return '--since=%s %s' % (conf['start_date'], commit_range)
    return commit_range

The way how getlogrange is implemented and called in other parts means commit_begin has no effect.
I propose the following fix:

1. Make start_date and commit_begin command line options mutually exclusive - only one of them can be defined. Error will be raised if both options are present.
2. Modify getxxxrange so that all combinations of start_date, commit_begin and end_only are handled correctly.

[rdkmaster]

any update?