dump: save registers when the task is already infected

Otherwise a task can start to handle a signal and registers can be
changed.
dump: return signal mask from parasite on initialization
parasite: remove extra synchronisation

crtools don't send a new command until it gets ack on a previous one.
restore: use a concrete object for constructing sigframe

struct thread_restore_args contains many pointers on different objects,
only a few of them are really required.
restore: add a function for constructing sigframe
restore: split restore_gpregs on two parts

The first one fills sigframe and the second one restores another
registers.
restore: construct sigframe in crtools

Before this patch sigframes were constructed in restorer. We are going
to construct sigframes for parasites. Both parasite and restorer should
be as thing as posible.
dump: fill sigblock mask immediately after getting it

It will be used for constructing sigframe for parasite threads
dump: reseve space and construc sigframes for parasites
parasite: transfer a pointer on sigframe to parasite
parasite: restore parasite state via rt_sigreturn

This patch reduces a window, when a crtools can kill a dumped process,
because if a parasite in a deamon mode can restore the state of the
process, if crtools detached unexpectedly.

All threads are synchronized on the exit point from sys_rt_sigreturn,
for that crtools traces all syscalls.
parasite: remove PARASITE_CMD_DAEMONIZED and s->ack
parasite: remove the hash table for tid_state-s

Use the same indexes which used for item->threads
parasite: don't store sig_blocked in a parasite