Format strings: don't ever convert %+d to %lu.

Presumably, if the printf format has the sign explicitly requested, the user
wants to treat the data as signed.

This is a fix-up for r172739, and also includes several test changes that
didn't make it into that commit.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@172762 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/PrintfFormatString.cpp b/lib/Analysis/PrintfFormatString.cpp
index 5d37de3..8f151b9 100644
--- a/lib/Analysis/PrintfFormatString.cpp
+++ b/lib/Analysis/PrintfFormatString.cpp
@@ -511,7 +511,7 @@
     case ConversionSpecifier::dArg:
     case ConversionSpecifier::DArg:
     case ConversionSpecifier::iArg:
-      if (QT->isUnsignedIntegerType())
+      if (QT->isUnsignedIntegerType() && !HasPlusPrefix)
         CS.setKind(clang::analyze_format_string::ConversionSpecifier::uArg);
       break;
     default: