less fails silently on bad import.

[connor4312]

I had a directory structure like:

project
 |-- css
     |-- bootstrap
     |   +-- import.less
     +-- style.less
 +-- bower_components

Style.less

@import 'bootstrap/imports';

Import.less

@import '../bower_components/bootstrap/less/variables.less';
// should have been:
// @import '../../bower_components/bootstrap/less/variables.less';

This was causing no file to be created by gulp-less, but no errors to be thrown.

[yocontra]

duplicate #118