propel-gen.bat different when installing Propel via Composer

Just moved away from a PEAR setup propel project and went to a composer based approach.

After installing propel1 using composer I recognized, that the `propel-gen.bat` contains:

```
@ECHO OFF
SET BIN_TARGET=%~dp0\"../propel/propel1/generator/bin"\propel-gen
bash "%BIN_TARGET%" %*
```

when running `vendor\bin\propel-gen.bat` it aborts with a `bash not found` error.