1.5.x: add an alternate Java directory path for OS X systems

Fixes this error with the 1.5.8 beta on OS X:

```
Searching for Board description file (boards.txt) ... FAILED
Board description file (boards.txt) not found. Searched in following places:
  - /Applications/Arduino.app/Contents/Resources/Java/hardware/**
  - /usr/local/share/arduino/hardware/**
  - /usr/share/arduino/hardware/**
```

In the meantime, you can fix the error with a symlink:

```sh
cd /Applications/Arduino.app/Contents/Resources
ln -s ../Java .
```