Several compilation and run-time problems occur when building on SGI

IRIX systems using the native compilers.  A summary is:
- Various files use "//" as a comment delimiter in c files.
- Problems caused by assuming "char" is signed.
  cash.in: building -signed the rules regression test fails as described
    in FAQ_QNX4.  If CHAR_MAX is "255U" then ((signed char)CHAR_MAX) is -1.
  postmaster.c: random number regression test failed without this change.
- Some generic build issues and warning message cleanup.

David Kaelbling

src/interfaces/odbc/psqlodbc.h

@@ -83,7 +83,7 @@ typedef UInt4 Oid;
 /*	Info limits */
 #define MAX_INFO_STRING		128
 #define MAX_KEYPARTS		20
-#define MAX_KEYLEN			512			//	max key of the form "date+outlet+invoice"
+#define MAX_KEYLEN			512			/*	max key of the form "date+outlet+invoice" */
 #define MAX_STATEMENT_LEN	MAX_MESSAGE_LEN