gdbserver: (#214909 c 82)

gdbserver: (#214909 c 82)

ensure proper cleanup of gdbsrv FIFOs/shmem files with untraced fork/exec

* syswrap-{generic|darwin|aix5}.c : in PRE(sys_execve) : terminate gdbserver
* pub_core_gdbserver.h and m_gdbserver.c : add VG_(gdbserver_prerun_action),
  factorising the actions to do by gdbserver at "startup" (i.e. a traced
  fork or a traced exec).
* scheduler.c : implement startup action using VG_(gdbserver_prerun_action)

(Philippe Waroquiers, philippe.waroquiers@skynet.be)

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@11771