Integer type policy

Integers are for numbers, enabling arithmetic like subtractions and for
loops without getting shot in the foot. Unsigneds are for bitfields.

- "int" for numbers that will always be laughably smaller than four
  billion, and where we don't care about the serialization format.

- "int32" for numbers that will always be laughably smaller than four
  billion, and will be serialized to four bytes.

- "int64" for numbers that may approach four billion or will be
  serialized to eight bytes.

- "uint32" and "uint64" for bitfields, depending on required number of
  bits and serialization format. Likewise "uint8" and "uint16", although
  rare in this project since they don't exist in XDR.

- "int8", "int16" and plain "uint" are almost never useful.

cmd/syncthing/gui.go

@@ -794,7 +794,7 @@ func toNeedSlice(fs []db.FileInfoTruncated) []map[string]interface{} {
 			"Version":      file.Version,
 			"LocalVersion": file.LocalVersion,
 			"NumBlocks":    file.NumBlocks,
-			"Size":         db.BlocksToSize(file.NumBlocks),
+			"Size":         db.BlocksToSize(int(file.NumBlocks)),
 		}
 	}
 	return output