T3.2 Serial2.end - handle alternate pins

On T3.2 if you do something like:
Serial2.setTX(31);
Serial2.setRX(26);
Serial2.begin(.9600);
...
Serial2.end();

It will on the end call will always reconfigure pins 9 and 10 to be
digital pins MUX = 1

teensy3/serial2.c

@@ -184,8 +184,18 @@ void serial2_end(void)
 	while (transmitting) yield();  // wait for buffered data to send
 	NVIC_DISABLE_IRQ(IRQ_UART1_STATUS);
 	UART1_C2 = 0;
-	CORE_PIN9_CONFIG = PORT_PCR_PE | PORT_PCR_PS | PORT_PCR_MUX(1);
-	CORE_PIN10_CONFIG = PORT_PCR_PE | PORT_PCR_PS | PORT_PCR_MUX(1);
+	switch (rx_pin_num) {
+		case 9: CORE_PIN9_CONFIG = PORT_PCR_PE | PORT_PCR_PS | PORT_PCR_MUX(1); break; // PTC3
+		#if !(defined(__MK64FX512__) || defined(__MK66FX1M0__))  // not on T3.4 or T3.5
+		case 26: CORE_PIN26_CONFIG = PORT_PCR_PE | PORT_PCR_PS | PORT_PCR_MUX(1); break; // PTE1
+		#endif
+	}
+	switch (tx_pin_num & 127) {
+		case 10: CORE_PIN10_CONFIG = PORT_PCR_PE | PORT_PCR_PS | PORT_PCR_MUX(1); break; // PTC4
+		#if !(defined(__MK64FX512__) || defined(__MK66FX1M0__))  // not on T3.4 or T3.5
+		case 31: CORE_PIN31_CONFIG = PORT_PCR_PE | PORT_PCR_PS | PORT_PCR_MUX(1); break; // PTE0
+		#endif
+	}
 	rx_buffer_head = 0;
 	rx_buffer_tail = 0;
 	if (rts_pin) rts_deassert();