Issue 286: --disable-coverage drops "-pthread" option

-pthread was added as part of setting up the gcov options
alloc loop now attempts an item_lock

Fixes a few issues with a restructuring... I think -M was broken before,
should be fixed now. It had a refcount leak.

Now walks up to five items from the bottom in case of the bottomost items
being item_locked, or refcount locked. Helps avoid excessive OOM errors for
some oddball cases. Those happen more often if you're hammering on a handful
of pages in a very large class size (100k+)

The hash item lock ensures that if we're holding that lock, no other thread
can be incrementing the refcount lock at that time. It will mean more in
future patches.

slab rebalancer gets a similar update.
item locks now lock hash table buckets

expansion requires switching to a global lock temporarily, so all buckets have
a covered read lock.

slab rebalancer is paused during hash table expansion.

internal item "trylocks" are always issued, and tracked as the hash power
variable can change out from under it.
remove global stats lock from item allocation

This doesn't reduce mutex contention much, if at all, for the global stats
lock, but it does remove a handful of instructions from the alloc hot path,
which is always worth doing.

Previous commits possibly added a handful of instructions for the loop and for
the bucket readlock trylock, but this is still faster than .14 for writes
overall.
README.md was missing from dist tarball
don't wait on condition without holding the lock

freebsd9 is the only platform that apparently cares about this.
Add some mild thread documentation

since reading the code is probably incredibly confusing now.
fix enable-sasl-pwdb

* using --enable-sasl-pwdb will make the compile fail with:

sasl_defs.c:148:4: error: initialization from incompatible pointer type [-Werror]
This adds the "shutdown" command to the server. This allows for better
automation (at least,... I find that it makes for better automation).
Merge pull request #22 from gabriel-samfira/master

Compile fails using enable-sasl-pwdb
Merge pull request #26 from trondn/brians-shutdown

This adds the "shutdown" command to the server. This allows for better
Fix make maintainer-clean
add aclocal 1.12 in autogen.sh