fix spec stubs to be absolute paths, since that's how /Users/yaauie/.rbenv/shims:/Users/yaauie/.rbenv/bin:/Users/yaauie/.bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin normally is.
use File::expand_path for joining PATH part with given executable name, thereby supporting absolute paths in the executable name
ensure each executable path only gets yielded once from find_executables; this is especially important when dealing with absolute path executables, which will match on every combination with /Users/yaauie/.rbenv/shims:/Users/yaauie/.rbenv/bin:/Users/yaauie/.bin:/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin part
provides a construct for blocking option-configs that don't make sense; uses that construct to prevent relative paths from being passed
1.8.x compatibility
Merge branch 'feature/support-absolute-path' into develop