[GH #71] remove test/misc/assign.pn, only for assign branch

this tests a new feture only being developed in the assign branch
fix cc on linux with missing clang
fix ignoring return value of ‘fwrite’

declared with attribute warn_unused_result.
return now NIL on fwrite errors with the print methods.
detected with centos
libuv: centos5 workaround
make: Recursive variable 'PLIBS' references itself
libuv: switch to my repo
aio: update to libuv 0.11.23, fix uv_buf_t

remove unneeded read2 part for pipes
fixed uv_buf_t argument
accept PNBytes and PNString as buf arguments
new PN_CHECK_STRB
one more Recursive variable 'PLIBS' references itself
fix 2 -Wnon-literal-null-conversion errors
config: refactor POTION_MAJOR.POTION_MINOR from potion.h to version.h

i.e. config.h. use it for windows LDFLAGS
update libuv to 0.11.23 dist
assertions and fixes recommended by Frama-C

all tests pass on 64bit
config.mak: disable -Werror, -Wno-zero-length-array -Wno-gnu
PN_F: do not return volatile long

volatile makes no sense as function return type, and gcc/clang warn about it.
warning: function return types not compatible due to volatile.
esp with -Werror

move PN_F up as it is used earlier
GC: fix ptr->vt < P->vts->len check for user objects

len < 100 but ptr->vt starts at PN_TNIL.
It caused example/binarytrees.pn errors
GC: found and fixed the last known GC bug

caused of course by simple typos/copy&paste and missing struct members.
copy now unknown (to the VM) words during gc_copy, instead of skipping them.
they will be unaccessible after the GC anyway, but we have no idea where they are
pointing to, or what the represent.
(missing volatile data, or extern .so data/ptrs might be a good guess).

example/binarytrees.pn passes now
compile-time ffi w/o sigs yet

sleep = extern sleep(n=n)
sleep(0.1)
extern: !dlsym just warns, create manual proto

no wrapper yet, not in the VM yet, just at compile-time
extern: add sample, start with arg handling
extern: add WITH_EXTERN config.h. not with SANDBOX

fix example