Disable SDK constraint checking on bleeding edge.

utils/pub/solver/backtracking_solver.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// A back-tracking depth-first solver. Attempts to find the best solution for
 /// a root package's transitive dependency graph, where a "solution" is a set
 /// of concrete package versions. A valid solution will select concrete
 /// versions for every package reached from the root package's dependency graph,
 /// and each of those packages will fit the version constraints placed on it.
 ///
@@ skipping 570 matching lines @@
       if (!package.descriptionEquals(required.ref)) return null;
     }
 
     return package;
   }
 }
 
 /// Ensures that if [pubspec] has an SDK constraint, then it is compatible
 /// with the current SDK. Throws a [SolverFailure] if not.
 void _validateSdkConstraint(Pubspec pubspec) {
+  // If the user is running a continouous build of the SDK, just disable SDK
+  // constraint checking entirely. The actual version number you get is
+  // impossibly old and not correct. We'll just assume users on continuous
+  // know what they're doing.
+  if (sdk.isBleedingEdge) return;
+
   if (pubspec.environment.sdkVersion.allows(sdk.version)) return;
 
   throw new CouldNotSolveException(
       'Package ${pubspec.name} requires SDK version '
       '${pubspec.environment.sdkVersion} but the current SDK is '
       '${sdk.version}.');
 }