Fix vim hang on xml files

TheĀ Syntastic syntax checking plugin validates xml files using xmllint.

You can pass custom arguments to xmllint to enable/disable functions that might be causing the hang.

For me it was the network access, which can be disabled with theĀ –nonet option.

I added the following to my ~/.vimrc

let g:syntastic_xml_xmllint_args = "--xinclude --postvalid --nonet"