Replace realpath with something Mac compat
Replace realpath with something Mac compat

Mac by default doesn't have realpath(1).
This replaces it with an equivalent bash script, so we can reduce script replacements on Homebrew.

Fixes #149

mdedetrich/sbt,sbt/sbt,xuwei-k/xsbt,mdedetrich/sbt,mdedetrich/sbt,mdedetrich/sbt,sbt/sbt,sbt/sbt,sbt/sbt,sbt/sbt,mdedetrich/sbt,sbt/sbt-launcher-package,xuwei-k/xsbt,sbt/sbt,sbt/sbt,mdedetrich/sbt,xuwei-k/xsbt,sbt/sbt-launcher-package,xuwei-k/xsbt,xuwei-k/xsbt,mdedetrich/sbt