Fix random build failure due to System.IO.FileSystem not found

[AArnott]

Applies fix for AArnott/CodeGeneration.Roslyn#25

[AArnott]

I see the Travis CI failure from this. Very odd as I wouldn't expect this to cause a build failure, and the failure in particular looks unrelated to the change. But I'll look more into it.

[AArnott]

I found a machine I could repro the problem on. I had forgotten that "no project info for P2P" is code for "the build failed on the referenced project".

[AArnott]

Evidently I inadvertently targeted a newer (1.0.5 instead of 1.0.4) version of the CoreCLR runtime.

[AArnott]

The Mac build failed due to what appears to be an unrelated issue:

[xUnit.net 00:01:19.0662249]     LibGit2Sharp.Tests.CheckoutFixture.CheckoutCurrentReference [FAIL]
[xUnit.net 00:01:19.0676401]       Assert.InRange() Failure
[xUnit.net 00:01:19.0677293]       Range:  (6/26/17 6:45:22 AM +00:00 - 6/26/17 6:45:22 AM +00:00)
[xUnit.net 00:01:19.0677729]       Actual: 6/26/17 6:45:21 AM +00:00
[xUnit.net 00:01:19.0694405]       Stack Trace:
[xUnit.net 00:01:19.0709012]         /home/travis/build/libgit2/libgit2sharp/LibGit2Sharp.Tests/TestHelpers/BaseFixture.cs(458,0): at LibGit2Sharp.Tests.TestHelpers.BaseFixture.AssertRefLogEntry(IRepository repo, String canonicalName, String message, ObjectId from, ObjectId to, Identity committer, DateTimeOffset before)
[xUnit.net 00:01:19.0710105]         /home/travis/build/libgit2/libgit2sharp/LibGit2Sharp.Tests/CheckoutFixture.cs(873,0): at LibGit2Sharp.Tests.CheckoutFixture.CheckoutCurrentReference()
Failed   LibGit2Sharp.Tests.CheckoutFixture.CheckoutCurrentReference
Error Message:
 Assert.InRange() Failure
Range:  (6/26/17 6:45:22 AM +00:00 - 6/26/17 6:45:22 AM +00:00)
Actual: 6/26/17 6:45:21 AM +00:00
Stack Trace:
   at LibGit2Sharp.Tests.TestHelpers.BaseFixture.AssertRefLogEntry(IRepository repo, String canonicalName, String message, ObjectId from, ObjectId to, Identity committer, DateTimeOffset before) in /home/travis/build/libgit2/libgit2sharp/LibGit2Sharp.Tests/TestHelpers/BaseFixture.cs:line 458
   at LibGit2Sharp.Tests.CheckoutFixture.CheckoutCurrentReference() in /home/travis/build/libgit2/libgit2sharp/LibGit2Sharp.Tests/CheckoutFixture.cs:line 873

Any ideas, @bording?

[AArnott]

This seems non-deterministic as well, since it passed on my own travis CI account.

[ethomson]

I'll kick it. I have yet to comprehend how we're ticking back in time but alas, we sometimes do.

[AArnott]

Thanks, @ethomson

[bording]

I've seen that kind of failure before. I wonder if its some sort of rounding/truncation error? For example, one code path rounds up to 22 seconds, and another truncates to 21.

[AArnott]

Ping?