clarify that vg-in-place cannot be used as an outer in outer/inner setup
If you use a vg-in-place outer, then you obtain errors such as:
valgrind: mmap(0x38000000, 3293184) failed in UME with error 22 (Invalid argument).
valgrind: this can be caused by executables with very large text, data or bss segments.

What must be used is the "make install"-ed valgrind



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13545 a5019735-40e9-0310-863c-91ae7b9d1cf9