fstools: update to the latest master branch

This is a big block(d) cleanup with new feature of generating "mount"
hotplug.d events.

It's an important update for those who were using mountd in the
pre-18.06 releases. Due to the mountd being replaced with blockd a
support for "mountd" hotplug.d events has been lost. It broke all kind
of shell scripts that were e.g. managing services depending on an
external USB drive availability.

This basically (re-)adds support for calling /etc/hotplug.d/mount/
scripts with ACTION ("add" or "remove") and DEVICE set.

af93f4b block(d): improve hotplug.d "mount" events for the autofs
3bb3352 blockd: unmount device explicitly when it disappears
28753b3 block: remove target directory after unmounting
c8c7ca5 block: cleanup handling "start" action of the "autofs" command
f1bb762 block: make blockd_notify() return an int instead of void
71c2bde block: generate hotplug.d mount events
30f5096 block: validate amount of arguments for the "autofs" command
dc6a462 blockd: don't reparse blob msg in the vlist callbacks
f6a9686 blockd: don't unmount device when removing it from the list
1913fea block: don't duplicate unmounting code in the mount_action()
6b445fa block: make umount_device() function more generic
a778468 block: don't duplicate mounting code in the mount_device()
5dc631d block: simplify code picking mount target directory
2971779 block: move blockd_notify() call out of the conditional blocks
b86bd6e block: fix formatting & indent in the mount_device()
e12c0d6 fstools: use EXIT_FAILURE when indicating error on exit
091aa3d fstools: guard usage of WEXITSTATUS

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
(cherry picked from commit 5c4277ec37)

package/system/fstools/Makefile

@@ -12,9 +12,9 @@ PKG_RELEASE:=3
 
 PKG_SOURCE_PROTO:=git
 PKG_SOURCE_URL=$(PROJECT_GIT)/project/fstools.git
-PKG_SOURCE_DATE:=2018-09-29
-PKG_SOURCE_VERSION:=29e53af0b91954ca6a13bdd1f0e67c939ccb8e6d
-PKG_MIRROR_HASH:=e90c60362dc3f304c9748b57a3e602f37fd758bf8134fbc3fbbda4300d4f46c7
+PKG_SOURCE_DATE:=2018-12-28
+PKG_SOURCE_VERSION:=af93f4b8dc32cf1320dfe8f4b93bb3a12606fc33
+PKG_MIRROR_HASH:=a2d8c2500fe75014ef16c039d8cdb276c1d5c066f8bce6550a3ecf46a9a411a9
 CMAKE_INSTALL:=1
 
 PKG_LICENSE:=GPL-2.0