wrapped ProjectReference to Microsoft.Scripting.Core in Choose

fix #1148
introduced DevelKey to be used for DEBUG builds
App.config depends on ConfigurationFlavor

Debug and Release have different PublicKeyToken
Updated version of IronPython
Merge pull request #1149 from paweljasinski/hg1148

wrapped ProjectReference to Microsoft.Scripting.Core in Choose
Merge pull request #1150 from paweljasinski/debug-key-app-config-split

debug assemblies are signed with different key
adjusted solution to reflect added removed files
Merge branch 'debug-key-app-config-split' into ipy-2.7-maint

missed an update to IronPython.sln