Test: CFPropertyList.propertyListFromXML.

These tests validate some basic edge cases with the parsing of XML plists.

Refs #2051.
Fixed: theoretical error while skipping whitespace in XML plists.

This fix ensures the PLIST_FIRST_CHILD() code gets to run both statements in the XML parsing while loop.

There's no obvious way to trigger an error due to this bug, but better correct than wrong.

Refs #2051.
Fixed: error in Internet Explorer if Info.plist was served with wrong content type.

Without this fix, in Internet Explorer the plist parser would only receive an empty XML document for the main Info.plist (and any other such loaded documents) if the server did not provide the content type "text/xml".

This fix parses the XML correctly even if there is no such content type.

Fixes #2051.