Add support for MacOS X (10.10)

[ankon]

• xargs -r: GNU extension, reimplemented using a shell function
• sed -z: GNU extension, reimplemented by piping through echo (removing
  the newlines) and tr (adding the ',')
• xargs -I{}: reimplemented using a for-loop, to avoid hitting
  the 255-byte limitation for eacho argument of xargs(1)

While there: replace the grep-parsing by a filtering for-loop, which
as a side-effect fixes command line arguments with quotes due to the use
of eval.

[Stephan202]

You basically rewrote it ;)

Good point on using tr(1). Will review the other changes later today and merge. Really a shame that cross-platform scripts always seem to boil down to reinventing the wheel :(.

[ankon]

"Hammered it into working in my environment" :)

[Stephan202]

Alright, added some notes. One last thing: we now have lower and upper-case variable names, as well as names with and without a leading underscore. Shall we settle on one style?