SIGNAL and SLOT macro are not threadsafe in Debug mode

In Debug mode, SIGNAL() and SLOT() are not threadsafe.

In Debug, the macro uses qFlagLocation():

1. define METHOD(a) qFlagLocation("0"#a QLOCATION)
2. define SLOT(a) qFlagLocation("1"#a QLOCATION)
3. define SIGNAL(a) qFlagLocation("2"#a QLOCATION)

First, this function use a static integer for the index:
static int idx = 0;
This variable is subject to race condition.

Secondly, the variable "flagged_locations" is global and is subject to race condition.

These two problem can lead to erroneous error message when a connection cannot be made. They can be corrected by using thread local storage for the two variable.