minor cleanup to the actions interface to pass around SmallVectorImpl instead

of a specific smallvector size.

Fix protocol lists to pass down proper location info, so we get diagnostics
like this:

t.m:3:35: error: cannot find protocol definition for 'NSCopying', referenced by 'NSWhatever'
@interface NSWhatever : NSObject <NSCopying>
                                  ^

instead of this:

t.m:3:44: error: cannot find protocol definition for 'NSCopying', referenced by 'NSWhatever'
@interface NSWhatever : NSObject <NSCopying>
                                           ^


Add a new IdentifierLocPair typedef which is just a pair<IdentifierInfo*, SourceLocation>

llvm-svn: 53883