Attempt to disable use of rwx memory for improved security

This should disable two different JIT engines inside of QT:

  QT_ENABLE_REGEXP_JIT disables the pcre JIT
  QV4_FORCE_INTERPRETER disables the QML JIT

There may be other QT JIT engines. On PaX/Grsecurity enabled
kernels, users will need to weaken their security by setting PaX flags:

  setfattr -n user.pax.flags -v "emr" /usr/bin/ricochet

In an ideal world, we will have no use of any JIT or JIT-like engine and
will be able to take full advantage of PaX related security features.

src/main.cpp

@@ -56,6 +56,11 @@ static void initTranslation();
 
 int main(int argc, char *argv[])
 {
+    /* Disable rwx memory.
+       This will also ensure full PAX/Grsecurity protections. */
+    qputenv("QV4_FORCE_INTERPRETER",  "1");
+    qputenv("QT_ENABLE_REGEXP_JIT",   "0");
+
     QApplication a(argc, argv);
     a.setApplicationVersion(QLatin1String("1.1.2"));
     a.setOrganizationName(QStringLiteral("Ricochet"));