Turn I/O error trapping on in HL7 code

By default, LGTM^%ZISTCP doesn't turn I/O error trapping on. This means that a lot of potential I/O errors (such as disconnects) are ignored in the HL7 code and require hacks to check for these error conditions. (See bug 526734 and bug 526609.)

We should turn on I/O error trapping in the HL7 code whenever $ETRAP is set. This will cause the normal error handlers to be invoked. We should also make sure that any checks in the HL7 error handlers that look for error codes or strings match GT.M-specific error codes and strings correctly.