[Resolver] Fix local pod platform conflict error

When resolver fails because of platform deployment target for a local pod,
`possibility` value is non-nil. We use this to discriminate this error type with
conflict caused by a change in dependencies of the local pod.

lib/cocoapods/resolver.rb

@@ -389,7 +389,6 @@ module Pod
         error.conflicts.each do |name, conflict|
           local_pod_parent = conflict.requirement_trees.flatten.reverse.find(&:local?)
           lockfile_reqs = conflict.requirements[name_for_locking_dependency_source]
-
           if lockfile_reqs && lockfile_reqs.last && lockfile_reqs.last.prerelease? && !conflict.existing
             message = 'Due to the previous naïve CocoaPods resolver, ' \
               "you were using a pre-release version of `#{name}`, " \
@@ -398,7 +397,7 @@ module Pod
               'version requirement to your Podfile ' \
               "(e.g. `pod '#{name}', '#{lockfile_reqs.map(&:requirement).join("', '")}'`) " \
               "or revert to a stable version by running `pod update #{name}`."
-          elsif local_pod_parent && !specifications_for_dependency(conflict.requirement).empty?
+          elsif local_pod_parent && !specifications_for_dependency(conflict.requirement).empty? && !conflict.possibility
             # Conflict was caused by a requirement from a local dependency.
             # Tell user to use `pod update`.
             message << "\n\nIt seems like you've changed the constraints of dependency `#{name}` " \

spec/unit/resolver_spec.rb

@@ -225,6 +225,21 @@ module Pod
         message.should.match /required a higher minimum deployment target/
       end
 
+      it 'raises an informative error when version conflict is caused by platform incompatibilities for local pods' do
+        sandbox = config.sandbox
+        local_spec = Specification.from_hash('name' => 'LocalPod', 'version' => '1.0', 'platforms' => { 'ios' => '8.0' })
+        sandbox.stubs(:specification).with('LocalPod').returns(local_spec)
+        @podfile = Podfile.new do
+          target 'SampleProject' do
+            platform :ios, '7.0'
+            pod 'LocalPod', :path => '../'
+          end
+        end
+        @resolver.stubs(:podfile).returns(@podfile)
+        message = should.raise(Informative) { @resolver.resolve }.message
+        message.should.match /required a higher minimum deployment target/
+      end
+
       it 'raises if unable to find a specification' do
         Specification.any_instance.stubs(:all_dependencies).returns([Dependency.new('Windows')])
         message = should.raise Informative do