eina_error: allow errno.h codes.

eina_error: allow errno.h codes.

we have some duplication of errors between Eina_Error and errno.h,
however we should use Eina_Error to extend the traditional errno.h
system.

then change eina_error_msg_register() and
eina_error_msg_static_register() to return a magic bit to state the
number was registered, and on other functions test this bit in order
to operate on registered values, otherwise fallback to errno.h, such
as strerror().

It also deprecates 2 clear duplicated errors:

- EINA_ERROR_OUT_OF_MEMORY -> ENOMEM

- EINA_ERROR_TIMEOUT -> ETIMEDOUT

There are two details when using strerror():

 - old behavior did not return strings for non-error, such as
   "Success" or "Unknown error ${N}"

 - thread-safety issues: since we must be thread safe, then use
   strerror_r() and eina_stringshare_add() that value, keeping a hash
   of cached values