failed attempt to use shared memory for the ip <-> dns mapping

this is in order to get irssi, which forks for DNS lookups,
and similar programs, to work as intended.

in a previous attempt i learned that shared memory created in a
child process is not visible to the parent;
in this attempt i spin off a thread from the parent which listens
on a pipe and manages the shared memory allocation from the parent
address-space. however this doesnt work as expected:
memory allocated in the parent after the child forked is not visi-
ble to the child as well.

so what happens is: irssi starts a child process, the thread allocs
memory and hands it to the child, the child attempts to write and
segfaults. however irssi doesnt crash. since now the memory is
already allocated, doing the dns lookup again will succeed.

i.e. the dns lookup works now in irssi by luck.
all but the first dns lookups will suceed.

however this is not good enough for me to be satisfied, i commit
this only for documentation purposes.

Makefile

@@ -15,7 +15,7 @@ sysconfdir=$(prefix)/etc
 
 SRCS = $(sort $(wildcard src/*.c))
 OBJS = $(SRCS:.c=.o)
-LOBJS = src/core.o src/common.o src/libproxychains.o
+LOBJS = src/core.o src/common.o src/libproxychains.o src/shm.o src/allocator_thread.o
 
 CFLAGS  += -Wall -O0 -g -std=c99 -D_GNU_SOURCE -pipe -DTHREAD_SAFE
 LDFLAGS = -shared -fPIC -Wl,--no-as-needed -ldl -lpthread