Fix enum error when value contains char in compound expression

Problem: When enum value contains compound expression with a char
constant, the quotes around char constant is missing in the generated
expression. Example:

enum media_type {
  YUY2 = ((('2' << 24) | ('Y' << 16)) | ('U' << 8)) | 'Y'
};

The generated C# enum becomes:

public enum media_type {
  YUY2 = (((2 << 24)|(Y << 16))|(U << 8))|Y
}

While the correct representation (after this fix) should be:

public enum media_type {
  YUY2 = ((('2' << 24)|('Y' << 16))|('U' << 8))|'Y'
}

Causes: the exprcompound promotes the expression type from char to int
and uses $1.val in the generated expression. However $1.val does not
contain the quotes. Since the type is promoted to int, there's no way to
know there's char component in the compound expression.

Solution: in exprcomound, use $1.rawval if $1.type is T_CHAR or T_WCHAR.
The rawval contains quotes which yield correct expression.

Source/CParse/cparse.h

@@ -78,4 +78,7 @@ extern "C" {
 #define SWIG_WARN_NODE_END(Node) \
   if (wrnfilter) Swig_warnfilter(wrnfilter,0); \
  }
+
+#define COMPOUND_EXPR_VAL(dtype) \
+  ((dtype).type == T_CHAR || (dtype).type == T_WCHAR ? (dtype).rawval : (dtype).val)
 #endif