Fix expension of macros in pointers with default values.

For example :

in xsl decl widget_class(%name, *clsname="%nameWidget", match="widget[@type='%name']", mode="widget_class") alias template {
| class `text **clsname` extends Widget{
content;
| }
};

widget_class('Input');

gives now :

<xsl:template match="widget[@type='Input']" mode="widget_class">
<xsl:text>class </xsl:text>
<xsl:text>InputWidget</xsl:text>
<xsl:text> extends Widget{
</xsl:text>
<xsl:text>}
</xsl:text>
</xsl:template>

Without the fix, <xsl:text>InputWidget</xsl:text> would be <xsl:text>%nameWidget</xsl:text>

[sdist]
formats=gztar

[metadata]
name         = yml2
version      = 2.7.0
author	     = Volker Birk
author_email = vb@pep-project.org
url	     = https://pep.foundation/dev/repos/yml2/
license	     = GPL v2
license_file = gpl-2.0.txt

[options]
packages = yml2
scripts =
    yml2c
    yml2proc
include_package_data = True
zip_safe = False
install_requires = lxml