Fix MS SQL tinyint identity support.

Add a cast rule to support tinyint being an “identity” type in MS SQL, which
means using a sequence to derive its values from. We didn't address the
whole MS SQL integer type tower here, and suspect we will have to add more
in the future.

Fix #528 where I could have access to a test case and easily reproduce the
bug, thanks!

Author: dimitri

src/sources/mssql/mssql-cast-rules.lisp

@@ -15,6 +15,11 @@
     (:source (:type "int" :auto-increment t)
              :target (:type "bigserial" :drop-default t))
 
+    (:source (:type "tinyint") :target (:type "smallint"))
+
+    (:source (:type "tinyint" :auto-increment t)
+             :target (:type "serial"))
+
     (:source (:type "bit") :target (:type "boolean")
              :using pgloader.transforms::sql-server-bit-to-boolean)
 
@@ -27,8 +32,6 @@
     (:source (:type "geography") :target (:type "bytea")
          :using pgloader.transforms::byte-vector-to-bytea)
 
-    (:source (:type "tinyint") :target (:type "smallint"))
-
     (:source (:type "float") :target (:type "float")
              :using pgloader.transforms::float-to-string)