libxml2 chucks errors

[thinkjson]

I get tons of errors that look like this when exiting the webshell:

xmlMemFree(201E5E0) error
xmlMallocBreakpoint reached on block 0
Memory tag error occurs :0x201e418
bye

[scoates]

We've taken libxml2 support out in 0.2; assigning to ehaas for cleanup before re-inclusion.