project cracker source files should contains .fsi

[enricosada]

using project cracker on a project with .fsi files, these are not returned in FSharpProjectOptions.Sourcefiles

this mean the need of ugly hack like https://github.com/fsharp/FsAutoComplete/blob/e5095da2b18da6fb6eb2fe7a9355d36e2fae9bf7/src/FsAutoComplete.Core/CompilerServiceInterface.fs#L359-L369 to put the .fsi files BEFORE the .fs files

[vasily-kirichenko]

Fixed in #812

[dsyme]

Now in master, thanks