libfuse: fix crash in unlock_path()

Patch by Ratna Manoj.

queue_element_unlock() should set ->first_locked and ->second_locked to false.

Discovered with 'fs_racer'.  The assert(wnode->treelock == TREELOCK_WRITE) in
unlock_path() was hit within minutes.

Miklos: simplified patch
libfuse: fix the 'remember' option

The lru list was not initialized for the "/" path.  This resulted in
remove_node_lru() crashing on LOOKUP-DOTDOT.

Patch by Madan Valluri.
--
 ChangeLog  |    4 ++++
 lib/fuse.c |    4 ++++
 2 files changed, 8 insertions(+)
libfuse: configure: detect new util-linux

Apparently new versions of util-linux umount return with an exit status of 1
even if the "--fake" option is recognised (despite being documented otherwise).
Check this condition and don't complain about util-linux version.
libfuse: Use AC_CONFIG_HEADERS instead of AM_CONFIG_HEADER

AM_CONFIG_HEADER has been deprecated for years and autotools 1.13
removes this macros at all.
libfuse: rename ./configure.in to ./configure.ac

Next version of automake (1.14) removes support for the deprecated filename

http://lists.gnu.org/archive/html/autotools-announce/2013-01/msg00000.html
Add "nopath" to help.
libfuse: fix thread cancel race

Exiting a worker my race with cancelling that same worker.  This caused a
segmenation fault.

Reported and tested by Anatol Pomozov
Add support for Clang
libfuse: fix multiple close of device fd

- fuse_kern_unmount closes handle (e.g. 19)
- a thread in my process opens a file - the OS assigns newly freed
handle (i.e. 19)
- fuse_kern_chan_destroy closes the same handle (i.e. 19)
- a thread in my process opens another file - the OS assigns newly
freed handle (i.e. 19)
- * MAYHEM *

Reported by Dan Greenfield
libfuse: don't close fd if it's -1

This prevents a valgrind warning.
Released 2.9.3
Do not hardcode install prefix in darwin_configure.sh

The install prefix can be set by defining the environment varialbe PREFIX. It
defaults to /usr/local.

Conflicts:
	darwin_configure.sh
Merge commit 'd44bf3a4ac1ce1b56672ac9ae4a5caa3a8ee6844'

Conflicts:
	lib/Makefile.am
	lib/fuse_kern_chan.c
(iconv, subdir, threadid, volicon) Add support for fallocate
(fusexmp_fh) Implement fallocate for OS X