Well this just pulled me out of a terrible hole ... the dreaded "case folding error" in Mercurial. The following advice worked:
And this seemed useful...
Failing over from CDN to local storage:
Twitter Bootstrap has a release candidate for version 3. Not sure how I feel about this yet. On the one hand the new stuff looks amazing, on the other, I'm not sure I like the new grid classes. But, worth a look and it is admirable that they are going for "mobile-first", so rolling the responsive stuff into the main build as default: