source index pdb files using SourceIndex

This will source index all pdb files in fsharp\lib\release. Any generated files are not source indexed. You must clone the repository with core.autocrlf set to input so that the line endings match.
```
git clone -config core.autocrlf=input https://github.com/fsharp/FSharp.git
./build.bat
./sourcelink.cmd
```
![image](https://f.cloud.github.com/assets/80104/2122633/24a73aa8-9216-11e3-9f6c-c0b4e53e6036.png)

![image](https://f.cloud.github.com/assets/80104/2122635/29150d5e-9216-11e3-9f5d-41fd0b765ed6.png)