Poke migration-management versions for 1.5.1-BETA3.

-packaging/build.xml already makes an update .sql from 1.5.1-BETA2,
the last released version. No change needed before this release.

Author: jcflack

pljava/src/main/java/org/postgresql/pljava/internal/InstallHelper.java

@@ -495,6 +495,7 @@ void migrateFrom( SchemaVariant sv, Connection c, Statement s)
 		UNREL20040120  ("5e4131738cd095b7ff6367d64f809f6cec6a7ba7"),
 		EMPTY          (null);
 
+		static final SchemaVariant REL_1_5_1_BETA3 = REL_1_5_0;
 		static final SchemaVariant REL_1_5_1_BETA2 = REL_1_5_0;
 		static final SchemaVariant REL_1_5_1_BETA1 = REL_1_5_0;
 		static final SchemaVariant REL_1_5_0_BETA3 = REL_1_5_0;