Makes conflicts fail faster

[mrinaldi]

This PR makes conflicts fail faster.

Take this paket.dependencies for example:

source https://nuget.org/api/v2

nuget Microsoft.AspNet.SignalR.JS
nuget Nancy.Serialization.JsonNet
nuget SourceLink.Fake
nuget Ninject.Extensions.Logging.Log4net == 3.2.0
nuget Ninject.Extensions.Interception.Linfu == 2.2.1.2

This is how paket is trying to resolve in 2.18.0:

Paket version 2.18.0.0
Resolving packages for group Main:
 - Ninject.Extensions.Logging.Log4net 3.2.0
 - Ninject.Extensions.Interception.Linfu 2.2.1.2
 - Microsoft.AspNet.SignalR.JS 2.2.0
 - Nancy.Serialization.JsonNet 1.3.0
 - SourceLink.Fake 1.1.0
 - jQuery 2.1.4
 - Nancy 1.3.0
 - Newtonsoft.Json 7.0.1
 - Ninject.Extensions.Interception 2.2.1.2
 - Ninject 2.2.1.4
 - Ninject.Extensions.Logging 3.2.3
 - Ninject.Extensions.Logging 3.2.2
 - Ninject.Extensions.Logging 3.2.1
 - Ninject.Extensions.Logging 3.2.0
 - Newtonsoft.Json 6.0.8
 - Newtonsoft.Json 6.0.7
 - Newtonsoft.Json 6.0.6
 - Newtonsoft.Json 6.0.5
 - Newtonsoft.Json 6.0.4
 - Newtonsoft.Json 6.0.3
 - Newtonsoft.Json 6.0.2
 - Newtonsoft.Json 6.0.1
 - Newtonsoft.Json 5.0.8
 - Newtonsoft.Json 5.0.7
 - Newtonsoft.Json 5.0.6
 - Newtonsoft.Json 5.0.5
 - Newtonsoft.Json 5.0.4
 - Newtonsoft.Json 5.0.3
 - Newtonsoft.Json 5.0.2
 - Newtonsoft.Json 5.0.1
 - Newtonsoft.Json 4.5.11
 - Newtonsoft.Json 4.5.10
 - Newtonsoft.Json 4.5.9
 - Newtonsoft.Json 4.5.8
 - Newtonsoft.Json 4.5.7
 - Newtonsoft.Json 4.5.6
 - Newtonsoft.Json 4.5.5
 - Newtonsoft.Json 4.5.4
 - Newtonsoft.Json 4.5.3
 - Newtonsoft.Json 4.5.2
 - Newtonsoft.Json 4.5.1
 - Newtonsoft.Json 4.0.8
 - Newtonsoft.Json 4.0.7
 - Newtonsoft.Json 4.0.6
 - Newtonsoft.Json 4.0.5
 - Newtonsoft.Json 4.0.4
 - Newtonsoft.Json 4.0.3
 - Newtonsoft.Json 4.0.2
 - Newtonsoft.Json 4.0.1
 - Newtonsoft.Json 3.5.8
 - jQuery 2.1.3
 - jQuery 2.1.2
 - jQuery 2.1.1
 - jQuery 2.1.0
 - jQuery 2.0.3
 - jQuery 2.0.2
 - jQuery 2.0.1.1
 - jQuery 2.0.1
 - jQuery 2.0.0
 - jQuery 1.11.3
 - jQuery 1.11.2
 - jQuery 1.11.1
 - jQuery 1.11.0
 - jQuery 1.10.2
 - jQuery 1.10.1
 - jQuery 1.10.0.1
 - jQuery 1.10.0
 - jQuery 1.9.1
 - jQuery 1.9.0
 - jQuery 1.8.3
 - jQuery 1.8.2
 - jQuery 1.8.1
 - jQuery 1.8.0
 - jQuery 1.7.2
 - jQuery 1.7.1.1
 - jQuery 1.7.1
 - jQuery 1.7.0
 - jQuery 1.6.4
 - SourceLink.Fake 1.0.0
 - SourceLink.Fake 0.6.1
 - SourceLink.Fake 0.6.0
 - SourceLink.Fake 0.5.0
 - SourceLink.Fake 0.4.2
 - SourceLink.Fake 0.4.0
 - SourceLink.Fake 0.3.4
 - SourceLink.Fake 0.3.3
 - SourceLink.Fake 0.3.2
 - SourceLink.Fake 0.3.1
 - SourceLink.Fake 0.3.0
 - Nancy.Serialization.JsonNet 1.2.0
 - Nancy 1.2.0
...

Note that it explores several versions from package that are not related to the conflict.
This is not the full output since I gave up after so many unrelated packages being explored.

This is how this PR is trying to resolve:

Paket version 2.18.0.0
Resolving packages for group Main:
 - Ninject.Extensions.Logging.Log4net 3.2.0
 - Ninject.Extensions.Interception.Linfu 2.2.1.2
 - Microsoft.AspNet.SignalR.JS 2.2.0
 - Nancy.Serialization.JsonNet 1.3.0
 - SourceLink.Fake 1.1.0
 - Ninject.Extensions.Logging 3.2.3
 - Ninject.Extensions.Interception 2.2.1.2
 - jQuery 2.1.4
 - Nancy 1.3.0
 - log4net 2.0.3
 - Newtonsoft.Json 7.0.1
 - Ninject.Extensions.Logging 3.2.2
 - Ninject.Extensions.Logging 3.2.1
 - Ninject.Extensions.Logging 3.2.0
Paket failed with:
        There was a version conflict during package resolution.
  Resolved packages:
   - Microsoft.AspNet.SignalR.JS 2.2.0
   - Nancy.Serialization.JsonNet 1.3.0
   - Ninject.Extensions.Interception 2.2.1.2
   - Ninject.Extensions.Interception.Linfu 2.2.1.2
   - Ninject.Extensions.Logging 3.2.0
   - Ninject.Extensions.Logging.Log4net 3.2.0
   - SourceLink.Fake 1.1.0
  Could not resolve package Ninject:
   - Ninject.Extensions.Interception 2.2.1.2 requested: >= 2.2.0.0 < 2.3.0.0
   - Ninject.Extensions.Logging 3.2.3 requested: >= 3.2.0.0 < 3.3.0.0

  Please try to relax some conditions.

[forki]