Added new action ChangeAccessModifierAction.
ChangeAccessModifierAction: Fixed bug that prevented action from being run on private accessors.
Fixed bug in ChangeAccessModifierActions: Action offered to modify accessors in virtual properties.
Merge branch 'luiscubal-access-modifier-actions' of https://github.com/mono-soc-2013/NRefactory into luiscubal-access-modifier-actions
ChangeAccessModifierAction now allows changing the modifier of virtual/override/new members. Since the action can cause compile errors anyway, there's no point in disabling it in this case.
Made ChangeAccessModifierAction less intrusive (use Script.ChangeModifier).
Merge branch 'luiscubal-access-modifier-actions' of github.com:mono-soc-2013/NRefactory into mono-soc-2013-luiscubal-access-modifier-actions

Conflicts:
	ICSharpCode.NRefactory.CSharp/ICSharpCode.NRefactory.CSharp.csproj
	ICSharpCode.NRefactory.Tests/ICSharpCode.NRefactory.Tests.csproj