Fixed bug reported by Marko Strukelj and Keith Wannamaker. Using executeBatch

on a preparedStatement would reset the prepared statment causing subsequent
uses of the preparedStatement to fail (i.e. the following series of calls
would fail: addBatch() executeBatch() addBatch() executBatch()).  This is
a regression from 7.2 where this worked correctly.  The regression test has
also been modified to explicitly test for this case.

 Modified Files:
 	jdbc/org/postgresql/jdbc1/AbstractJdbc1Statement.java
 	jdbc/org/postgresql/jdbc2/AbstractJdbc2Statement.java
 	jdbc/org/postgresql/test/jdbc2/BatchExecuteTest.java