Added an assert to IntegerLiteral to ensure that the integer type passed in...

Added an assert to IntegerLiteral to ensure that the integer type passed in has the same size as the APInt passed in.  Also, updated the comments around IntegerLiteral.

Changed the integer type that range-based for-loops used.  Switched to pointer difference type, which satisfies the new assert in IntegerLiteral.

llvm-svn: 130739