[Patch] Fix enum type mismatch

Attached patch fixed following warning:

"../../../src/include/nodes/parsenodes.h", line 487: warning: enumerator
value overflows INT_MAX (2147483647)

The reason is clear, enum is int not unsigned.

It is short fix, but I'm thinking about enum conversion to #define. We
use e.g. in the same file.

60 typedef uint32 AclMode; /* a bitmask of privilege bits */
61
62 #define ACL_INSERT (1<<0) /* for relations */
63 #define ACL_SELECT (1<<1)
64 #define ACL_UPDATE (1<<2)
65 #define ACL_DELETE (1<<3)
66 #define ACL_TRUNCATE (1<<4)
67 #define ACL_REFERENCES (1<<5)
68 #define ACL_TRIGGER (1<<6)

Zdenek