use name transactions (savepoints) for sqlite transactions

Pg_qlite_begin and Pg_sqlite_commit are functions used by the Pgtcl pg_sqlite command to begin and commit transactions in sqlite. They used to just do a sqlite "begin" and "commit", but we now swap them to use a named transaction via "savepoint pg_sqlite;" and "release savepoint pg_sqlite;".

This allows the import of postgres results using pg_sqlite to occur within an outer sqlite transaction.

Version bump to 2.6.2.

* https://www.sqlite.org/lang_transaction.html
* https://www.sqlite.org/lang_savepoint.html

configure.in

@@ -19,7 +19,7 @@ dnl	to configure the system for the local environment.
 # so you can encode the package version directly into the source files.
 #-----------------------------------------------------------------------
 
-AC_INIT([pgtcl], [2.6.1])
+AC_INIT([pgtcl], [2.6.2])
 
 #-----
 # Version with patch stripped

generic/pgtclSqlite.c

@@ -62,7 +62,7 @@ int
 Pg_sqlite_begin(Tcl_Interp *interp, sqlite3 *sqlite_db)
 {
 	char *errMsg;
-	if(sqlite3_exec(sqlite_db, "begin;", NULL, NULL, &errMsg) != SQLITE_OK) {
+	if(sqlite3_exec(sqlite_db, "savepoint pg_sqlite;", NULL, NULL, &errMsg) != SQLITE_OK) {
                 Tcl_AppendResult(interp, errMsg, " when beginning a transaction", (char *)NULL);
                 return TCL_ERROR;
         }
@@ -73,7 +73,7 @@ int
 Pg_sqlite_commit(Tcl_Interp *interp, sqlite3 *sqlite_db)
 {
 	char *errMsg;
-	if(sqlite3_exec(sqlite_db, "commit;", NULL, NULL, &errMsg) != SQLITE_OK) {
+	if(sqlite3_exec(sqlite_db, "release savepoint pg_sqlite;", NULL, NULL, &errMsg) != SQLITE_OK) {
                 Tcl_AppendResult(interp, errMsg, " when comitting a transaction", (char *)NULL);
                 return TCL_ERROR;
         }