pgtype Int2, Int4, and Int8 fields include bit size

e.g. Instead of Int it is Int64. This matches the pattern set by the
database/sql types.

pgtype/zeronull/int.go

@@ -44,7 +44,7 @@ func (dst *Int2) Scan(src interface{}) error {
 		return err
 	}
 
-	*dst = Int2(nullable.Int)
+	*dst = Int2(nullable.Int16)
 
 	return nil
 }
@@ -92,7 +92,7 @@ func (dst *Int4) Scan(src interface{}) error {
 		return err
 	}
 
-	*dst = Int4(nullable.Int)
+	*dst = Int4(nullable.Int32)
 
 	return nil
 }
@@ -140,7 +140,7 @@ func (dst *Int8) Scan(src interface{}) error {
 		return err
 	}
 
-	*dst = Int8(nullable.Int)
+	*dst = Int8(nullable.Int64)
 
 	return nil
 }

pgtype/zeronull/int.go.erb

@@ -45,7 +45,7 @@ func (dst *Int<%= pg_byte_size %>) Scan(src interface{}) error {
 		return err
 	}
 
-	*dst = Int<%= pg_byte_size %>(nullable.Int)
+	*dst = Int<%= pg_byte_size %>(nullable.Int<%= pg_bit_size %>)
 
 	return nil
 }