Edited Issue: fsi build.fsx execution leads to error FS0193: internal error: Value cannot be null. Parameter name: con [88]

Product and OS versions as detailed in [issue 87](https://rdotnet.codeplex.com/workitem/87)

using
```
Revision: 253
Changeset: f8e3bd4164f0830641a4742d57524fbd90471dca [f8e3bd4164f0]
Parents: 252
Date: Tuesday, 25 February 2014 12:15:36 PM
```
and using /cygdrive/c/Program Files (x86)/Microsoft SDKs/F#/3.1/Framework/v4.0/fsi

```
F:\codeplex\rdotnet\tools>fsi build.fsx --help
error FS0193: internal error: Value cannot be null.
Parameter name: con
```

Note that with the open source edition, built from the following commit, there is no issue:
```
Commit: 0d2ee58db4967387cf8a7ae5d1c7f00b34137f6b [0d2ee58]
Parents: 4fe4e38d81, 2b2c2ba9bc
Author: Don Syme <donsyme@fastmail.fm>
Date: Friday, 21 February 2014 8:35:40 PM
Labels: HEAD, origin/master, origin/HEAD, master
Merge pull request #272 from enricosada/autogen_diagnostics

add diagnostics message to autogen.sh
```

Possible workarounds:
* use the open source F# tools,
* test whether one should use Fake.exe instread, as described [here](https://github.com/fsharp/FAKE/issues/113)