Build bootstrap-ie6 for incorrect margin-left of .offset*

I build bootstrap-ie6 less files.

But there's something I have to explain:

* the real modifications is just [those 12 lines](https://github.com/Witcher42/bsie/compare/ddouble:master...master#diff-c7c2085b0e39586cf07a12bcdedcb2c7L205)
* the last modifications are about blank spaces and typography **except one**
* the [exceptional one](https://github.com/Witcher42/bsie/compare/ddouble:master...master#diff-c7c2085b0e39586cf07a12bcdedcb2c7L4852) is about height of `carousel-inner img`, which is added but not built. I didn't test this, hope this doesn't matter.