Some changes for both OS X and Linux systems.

*__NOTE:
Don't feel pressured to accept this. I'd be happy with whatever feedback you have regarding the changes I've made.__*

## Makefile.mac
- New makefile based on your original one, tested to work under vanilla OS X 10.9.
- No longer uses echo escape sequences.
- install commands no longer use -D flag (there does not seem to be an equivalent in BSD install... correct me if wrong).
- Included changes made in main Makefile (listed below).

*Not sure if having a separate makefile for OSX/BSD is the best way to go about it, or just integrate it into the original Makefile and somehow differentiate between commands depending on the host system (as the underlying script logic is the same).*

## Makefile
- Fixed uninstall target to remove the compatibility symlink made when running the install target.
- Added clean target to remove the version produced script from the "all" target.
- Removed double forward slash in command in uninstall target (this seemed like a typo, although if there was a reason, let me know).
- Tested to work using GNU make 4.0 under most recent Arch Linux installation image.

## INSTALL
- Added note to BUILDING paragraph for OSX/BSD users regarding new Makefile.
- Fixed minor grammatical error.

## common/hosts-update.in
- Checks if system is OS X, and if so, leaves all the echo escape sequences unset (as default echo in OS X doesn't support them and it just ends up looking yuck).
- Fixed minor spelling mistake.