Deal with alternating headers

[webmaster128]

As part of #179, alternating headers do not hit anymore. This is because in case of a changed header, a new manifest is created instead of updating the old one.

A (small) manifest looks like this

{
  "includeFiles": {
    "c:\\program files (x86)\\microsoft visual studio 14.0\\vc\\include\\concurrencysal.h": "cf7c28041ac710f2f4e8e03184ceb03a",
    "c:\\program files (x86)\\microsoft visual studio 14.0\\vc\\include\\sal.h": "25992979c3dc319b2b22111261d8b4ba",
    "c:\\program files (x86)\\microsoft visual studio 14.0\\vc\\include\\vadefs.h": "303c50a7bc924cd426baa20c7f16192c",
    "c:\\program files (x86)\\microsoft visual studio 14.0\\vc\\include\\vcruntime.h": "70f6d71b7615fc31611118aaa55f403d",
    "c:\\program files (x86)\\windows kits\\10\\include\\10.0.10240.0\\ucrt\\corecrt.h": "c18832d918808d40b4664a51a8824a51",
    "c:\\program files (x86)\\windows kits\\10\\include\\10.0.10240.0\\ucrt\\corecrt_stdio_config.h": "035d8ef27e5026070e7650ea137714a0",
    "c:\\program files (x86)\\windows kits\\10\\include\\10.0.10240.0\\ucrt\\corecrt_wstdio.h": "2443db19dcc585e308f60dafef1d4c4c",
    "c:\\program files (x86)\\windows kits\\10\\include\\10.0.10240.0\\ucrt\\stdio.h": "2d5e699df1bed89fcccccf0dcfc49050"
  },
  "includesContentToObjectMap": {
    "b9e261c1d8ead6f14fe04c9e287abd1b": "20bde61f68b678191e2dff48321984a0"
  }
}

This manifest contains hashes of all includes as a map. In order to fix this, multiple file hashes per include must be allowed.

Given that there are no sets in JSON, includeFiles will need to become a dictionary from string to lists of strings.

As long as the include content equals one of the hashes, everything is fine and the manifest can be used. The actual include content is encoded in the includesContentToObjectMap key.

As soon as one include hash is not included, it becomes tricky: then we must deal with one manifest having multiple includes lists.

Dealing with multiple includes list per manifest is likely to be very painful. So I'll just start with a failing test.

[webmaster128]

Interesting. This was not supposed to hit #155. But well, it does. Fine, let's do that first.

[siu]

I started working in #222 to solve the race condition updating the manifests but along the way I found that it was easy to work on these issues too. I cherry-picked your unit tests there too.

[webmaster128]

Sure, feel free. I did not start working on this yet. However, I don't think it is wise to use the test as long as #155 is not fixed, since the test currently fails for the wrong reason. But I did not dig into #222, so you might already have taken this into account.

[webmaster128]

Closing this in favor of other people's solutions. I did not start working on an implementation yet.