#1291 Change default table border css properties

[Jan Tosovsky]

My table with defined css borders was rendered still without border lines. Later I found that some browsers don't render sub-pixel border lines (Chrome).
To avoid similar confusion in the future I suggest changing the following defaults from 0.5pt to 1px:
<xsl:param name="table.cell.border.thickness">0.5pt</xsl:param>
<xsl:param name="table.frame.border.thickness">0.5pt</xsl:param>

Thanks.

[Robert Stayton]

That param is used for both fo and html outputs, so just setting it to 1px would make the rule lines too thin for PDF output. I changed the param to use xsl:choose so it can apply 1px for html outputs and 0.5pt for other outputs.