Fix xslt error parsing so filename and line numbers show.

[lambdafu]

This is worth a 🤦 ...

Before:

<string>:0:0:ERROR:XSLT:ERR_OK: compilation error, element 'foo'
<string>:0:0:ERROR:XSLT:ERR_OK: xsltStylePreCompute: unknown xsl:foo
<string>:0:0:ERROR:XSLT:ERR_OK: compilation error, element 'foo'
<string>:0:0:ERROR:XSLT:ERR_OK: xsltParseStylesheetTop: unknown foo element

After:

errtest.xml:3:0:ERROR:XSLT:ERR_OK: compilation error, element 'foo'
<string>:0:0:ERROR:XSLT:ERR_OK: xsltStylePreCompute: unknown xsl:foo
errtest.xml:3:0:ERROR:XSLT:ERR_OK: compilation error, element 'foo'
<string>:0:0:ERROR:XSLT:ERR_OK: xsltParseStylesheetTop: unknown foo element

We can't do better, as the second line in the two errors embellishes the first line and does not duplicate the file/line info.

Example:

from io import BytesIO
from lxml import etree
style = etree.parse("errtest.xml")
try:
    etree.XSLT(style)
except etree.XSLTParseError as e:
    print e.error_log

[lambdafu]

Oh, here is the xslt:

<xsl:stylesheet version="1.0"
    xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:foo />
</xsl:stylesheet>

It's really the same from the test case that's already there (but which only checks for presence of ERROR:XSLT).

[scoder]

Ah, beautiful. Thanks!