Change geant4 to cern_it1.
Fields to keep track of newly created threads.
Never hang on wait4.

Parrot would block waiting for the parent of a particular thread to wake
up. Such thread, however, was stopped since it was recently created;
additionally, for some reason remained stopped after a SIGCONT. In this
fix, we let parrot continue, and wait on a usleep. This allow to resend
the lost SIGCONT in a further loop iteration.
Hack to wake sleepy threads.

When a thread is newly created using ptrace, parrot is notified of a
SIGSTOP on the thread. Under normal circumstances parrot sends a SIGCONT
to the thread, and we are all happy.

The problem here is that the thread does not receive that SIGCONT. Here
we add newly created threads to a set, and send them SIGCONTs at most
every second until they wake up.
Use ptrace options to follow children.

This is a possible fix to Parrot missing events for multi-threaded processes.
wait for child to start
Use EXITKILL ptrace option to ensure cleanup.

This is just an extra measure on top of what we already do using the watchdog
and signal handling.

Fixes #28.
Only modify fork/clone if necessary.
Continue the tracee after attaching.
Remove wq_reset since there is no visible use-case.
Internally, release_all_workers() can be used to achieve the same function.
add user munual for parrot_pack env_process create_mountlist
Revert minor whitespace changes.
Wake up stopped threads in Parrot.

* PR-470:
  Revert minor whitespace changes.
  Hack to wake sleepy threads.
  Never hang on wait4.
  Fields to keep track of newly created threads.
  Change geant4 to cern_it1.
rm parrot/src/README.pack
Merge master.

Conflicts:
	parrot/src/pfs_main.cc
add parrot_pack env_process create_mountlist into SEE_ALSO_PARROT
Add documentation for parrot packaging facilities.

* ccl/pull/476/head:
  add parrot_pack env_process create_mountlist into SEE_ALSO_PARROT
  rm parrot/src/README.pack
  add user munual for parrot_pack env_process create_mountlist
Add parrot_pack to .gitignore.
Silece unused variable warning.
Use itable to avoid compiler warning.

I don't see an easier way around this warning from gcc 4.9.0:

COMPILE pfs_main.o
pfs_main.cc: In function ‘void handle_event(pid_t, int, rusage*)’:
pfs_main.cc:356:47: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
       set_insert(stopped_threads, (void *) p->pid);
                                               ^
cc1plus: all warnings being treated as errors
../../Makefile.rules:9: recipe for target 'pfs_main.o' failed

Introduced in 97fb3f42713be6a5698b6e4d0ddcc5e700155dd9.