Escape characters now print a tab instead of "\t" on both install.sh and mac_install.sh

When echo-ing text using \t in it, it just printed the \t instead of the actual tab, so I fixed it using a function called `ECHO` that just takes the message and prints it with the -e flag. Now, instead of having to write `echo -e` all the time, one can just use `ECHO`.

This is fixed on the Linux and OS X install. Tested on CentOS and OS X Mountain Lion.