graph image cutoff first digits when Y axis has decimals #2804

The API's ImageGraph works fine when numbers along the Y axis are all whole numbers, but when one of them has a decimal point (ie, 1.5, 0.5) the first digit and the decimal number get cut off the side of the image, like so
http://demo.piwik.org/index.php?module=API&method=ImageGraph.get&idSite=3&apiModule=VisitsSummary&apiAction=get&token_auth=anonymous&graphType=evolution&period=day&date=2011-11-26&width=500&height=250&segment=country==DE

Attachment:
Screen shot 2011-11-28 at 12.49.40 PM.png

(In [5582]) * fixes #2706, #2828, #2704, refs #1721, #2637, #2711, #2318, #71 : horizontal static graph implemented

• fixes #2788, refs #2670, #1721, #2637, #2711 : default graph type logic moved to ImageGraph API, improved date/period logic, new parameter graphs_default_period_to_plot_when_period_range
• fixes #2704, #2804, refs #1721 : pChart updated to 2.1.3, pChart code removed from Piwik code, OOP refactoring, support for unifont.ttf if present in ImageGraph/fonts, testAllSizes now uses report metadata ImageGraphUrl
• refs #5491 : space between report title and report table reduced to avoid page overflow
• refs #2829 : TODO display percentages
• r5544, r5547, r5549 merged