Created inlined integer_hash_fast() and pointer_hash_fast() versions.
Switched from hashing_fold() to new hashing_keep() for hash table indexing.

The rationale is that we assume the hashing function is good and therefore
disperses correctly among all the bits.  Therefore, folding will only
marginally help achieve more diffusion, if any, and will not guarantee that
conflicts will not remain when the table size is increased.
guess_pick_next(): skip hosts to which we are already connected.
check_leaf_list_consistency(): display faulty knode when assertion fails.
forget_merged_node(): was incorrectly resetting status to KNODE_UNKNOWN.

This lead to assertion failures later in free_node_lists() when the old
(now merged) buckets were disposed of, because the nodes that were not kept
failed to bear the proper status in their respective list, an error caught
by check_leaf_list_consistency().

For security, added checks about the list consistency in merged_node_list()
to verify that the two lists we are merging are already holding nodes with
the correct status.
Added http_async_url() and friends to avoid using http_async_info() with NULLs.
Revised procedure to update sourceforge's home page after a release.
Renamed some of the THREAD_LOCK and THREAD_UNLOCK calls to be file-specific.

This avoids ctags conflicts, and is clearer.
Regenrated Configure and Makefiles for the pthread compiler switch.
signal_abort(): marked as "noreturn" function, and log raise() error if any.
Added s_error_expr() to be able to use it in comma-separated expressions.
Moved machine register access macros to lib/registers.h.
Added mem_protection(), mem_is_writable() and mem_is_writable_range().
Made memory checking thread-safe.
parse_base(): was not parsing a plain "0" correctly.
Added Windows emulation for the sleep() routine.
Reverted walloc() to use global (shared) zones for all block sizes.

This partially undoes what commit 0935821c73bff3a1282279837b453d56d2b2c469
introduced: we continue to let zalloc() handle private zones but the walloc()
wrapper is meant for general allocations and no longer requests private zones.

Indeed, it is far too difficult to guarantee that only the thread which
allocated a block with walloc() will be the one that wfree() it later. Adding
runtime checks would complicate the zalloc() and zfree() logic to the point
that it would probably alleviate the benefits of using thread-private zones
in the first place.

Now we retain the ability to request private zones for threads which will
do their own zalloc() and where it is easier to formally guarantee thread
safety via code proof-reading.
Documented why we must not use hidden spinlocks for zalloc() zone locks.
Added public mutex_is_valid() check.
Added THREAD_NONE definition, indicating "no thread".