Change "an problem" to "a problem" in .po files.
Change "an problem" to "a problem" in .py files.
Replace "a exercise" with "an exercise" in .po and .py files
Change 'Problemed' to 'Posted a problem to'

But manually change replacements that don't make sense.
add to cart bug fix
Merge pull request #172 from yingmao/master

cart bug fixed
Merge pull request #175 from objcow/master

Added missing file
Fixed mathjax rendering. Again.