fix for huge inefficiency in form model when dealing when initializing very large XML instances
tightened up selector for itemsets to update, #92
bind (upgraded) XPath evaluator to XMLDocument.prototype and properly call evaluate() on instance of XMLDocument instead of instance of HTMLDocument
experiment: first try native evaluation, if fails try non-native evaluation
check if expr contains custom OpenRosa before trying native
Merge branch 'master' of https://github.com/MartijnR/enketo-core into performance_cascades
a bit of cleanup
return array of elements if evaluate resultType is 'nodes'
Merge branch 'performance_cascades'