[#1259] Fixes a JS error with autocomplete module and improves UX

1. Basically adds an extra check to make sure that 'abort()' is
defined
2. Then changes the module to behave a little nicer when inbetween
ajax requests
[#1259] Remove redundant callback definition
Merge pull request #1259 from okfn/1259-autocomplete-fixes

Autocomplete JS module issues