jQueryUiFiles1.10: recursive docFiles with no dirs

API documentation for jQuery UI 1.10 now has subdirectories. So, find docFiles
recursively, and skip directories from the list.
Gruntfile: Build API docs with `grunt build`

Simply use `grunt build` instead of explicitly call the pieces with `grunt
build-pages build-xml-entries build-xml-categories` to build the API
documentation for jQuery UI.