Argument handling is not transparent on Windows

[alamaison]

When arguments contain quotes on Windows, they are not passed to the program correctly because the argument handling in Boost.Process 0.5 is naive. Currently, it just checks to see if an argument has a space in it and, if so, surround the argument with quotations. This breaks if the argument itself contains quotations.

The previous version of Boost.Process did not have this problem.