Fixes trac:2812: check for env. markers indicating that we're in a

fakeroot.  If so, exit out of the pre-main hook immediately (without
calling functions such as stat, which will be replaced by fakeroot to
things that are not safe to call in a pre-main environment).

This commit was SVN r26203.

The following Trac tickets were found above:
  Ticket 2812 --> https://svn.open-mpi.org/trac/ompi/ticket/2812

opal/mca/memory/linux/hooks.c

@@ -738,7 +738,17 @@ static void opal_memory_linux_malloc_init_hook(void)
     check_result_t r1, r2, lp, lpp;
     bool want_rcache = false, found_driver = false;
 
-    /* First, check if ummunotify is present on the system. If it is,
+    /* First, check for a FAKEROOT environment.  If we're in a
+       fakeroot, then stat() (and likely others) have been replaced
+       and are not safe to call here in this pre-main environment.  So
+       check for the environment markers that we're in a FAKEROOT.
+       And if so, return immediately. */
+    if (getenv("FAKEROOTKEY") != NULL ||
+        getenv("FAKE_ROOT_MODE") != NULL) {
+        return;
+    }
+
+    /* Next, check if ummunotify is present on the system. If it is,
        then we don't need to do the following ptmalloc2 hacks.
        open/mmap on the device may fail during init, but if /dev/ummunotify
        exists, we assume that the user/administrator *wants* to use