fix: avoid memory leak when redeploying pgjdbc

FAST_NUMBER_FAILED is used as a control-flow-exception pattern, thus it does not require a stacktrace.
It turns out Throwable might store strong reference to a class, thus it might result in OutOfMemory

closes #394

org/postgresql/jdbc2/AbstractJdbc2ResultSet.java

@@ -2217,7 +2217,18 @@ public long getLong(int columnIndex) throws SQLException
      * the exception is always caught and is not visible to users.
      */
     private static final NumberFormatException FAST_NUMBER_FAILED = 
-        new NumberFormatException();
+        new NumberFormatException() {
+
+            // Override fillInStackTrace to prevent memory leak via Throwable.backtrace hidden field
+            // The field is not observable via reflection, however when throwable contains stacktrace, it does
+            // hold strong references to user objects (e.g. classes -> classloaders), thus it might lead to
+            // OutOfMemory conditions.
+            @Override
+            public synchronized Throwable fillInStackTrace()
+            {
+                return this;
+            }
+        };
 
     /**
      * Optimised byte[] to number parser.  This code does not