Comment 9 for bug 591948

The attached patch applies to lib/graphite/render/glyph.py
=> it is written based on 0.96 version

It fixes:
1/ labels being displayed
2/ x minor and major grid line generation:
     * time grid lines no longer appear shifted in graphs
     * pbs occurring when minor/major grid lines should align and do not due to python float precision issues

As mentioned in an earlier comment, i ported the find_first_time/find_next_time functions available in rrdtool graph source code and adapt it.