Proposal: Add Bootstrap sprockets include

For applications which are using bootstrap-sass 3.2 in production (or not using asset pipeline), precompiled glyphicon paths will be incorrect without this line. This does break the tests, and would also really need to encompass locking down bootstrap-sass to 3.2 (also looking into any updates that 3.2 introduces).

https://github.com/twbs/bootstrap-sass/issues/653