fix argument quoting on windows

quotes prefixed with multiple backslashes would not be escaped
correctly.

Change-Id: I56ec72e31bb4ed2b9119ec1996448f803f89ce35
Reviewed-on: http://codereview.qt.nokia.com/962
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@nokia.com>

src/corelib/io/qprocess_win.cpp

@@ -46,6 +46,7 @@
 #include <qdatetime.h>
 #include <qdir.h>
 #include <qfileinfo.h>
+#include <qregexp.h>
 #include <qtimer.h>
 #include <qthread.h>
 #include <qmutex.h>
@@ -256,10 +257,8 @@ static QString qt_create_commandline(const QString &program, const QStringList &
 
     for (int i=0; i<arguments.size(); ++i) {
         QString tmp = arguments.at(i);
-        // in the case of \" already being in the string the \ must also be escaped
-        tmp.replace( QLatin1String("\\\""), QLatin1String("\\\\\"") );
-        // escape a single " because the arguments will be parsed
-        tmp.replace( QLatin1Char('\"'), QLatin1String("\\\"") );
+        // Quotes are escaped and their preceding backslashes are doubled.
+        tmp.replace(QRegExp(QLatin1String("(\\\\*)\"")), QLatin1String("\\1\\1\\\""));
         if (tmp.isEmpty() || tmp.contains(QLatin1Char(' ')) || tmp.contains(QLatin1Char('\t'))) {
             // The argument must not end with a \ since this would be interpreted
             // as escaping the quote -- rather put the \ behind the quote: e.g.