Switch from YAJL to Jansson

While YAJL mostly works fine, it did not see any active development in
the last 3 years.  OTOH, Jansson is another JSON C implementation, with
a very liberal license, and a much nicer API.

Hence, switch all of libguestfs from YAJL to Jansson:
- configure checks, and buildsystem in general
- packages pulled in the appliance
- actual implementations
- contrib scripts
- documentation

This also makes use of the better APIs available (e.g. json_object_get,
json_array_foreach, and json_object_foreach).  This does not change the
API of our OCaml Yajl module.

contrib/p2v/aux-scripts/do-build.sh

@@ -53,8 +53,8 @@ case $osversion in
         # This just forces configure to ignore these missing dependencies.
         export LIBTINFO_CFLAGS=-D_GNU_SOURCE
         export LIBTINFO_LIBS=-lncurses
-        export YAJL_CFLAGS=-D_GNU_SOURCE
-        export YAJL_LIBS=-lyajl
+        export JANSSON_CFLAGS=-D_GNU_SOURCE
+        export JANSSON_LIBS=-ljansson
         # Remove some unsupported flags that the configure script hard codes.
         sed -i -e 's/-fno-strict-overflow//' configure
         sed -i -e 's/-Wno-strict-overflow//' configure
@@ -66,8 +66,8 @@ case $osversion in
         # This just forces configure to ignore these missing dependencies.
         export LIBTINFO_CFLAGS=-D_GNU_SOURCE
         export LIBTINFO_LIBS=-lncurses
-        export YAJL_CFLAGS=-D_GNU_SOURCE
-        export YAJL_LIBS=-lyajl
+        export JANSSON_CFLAGS=-D_GNU_SOURCE
+        export JANSSON_LIBS=-ljansson
         ;;
 esac
 

contrib/p2v/build-p2v-iso.sh

@@ -86,7 +86,6 @@ done
 # Various hacks for different versions of RHEL.
 if=virtio
 netdev=virtio-net-pci
-pkgs="$pkgs,yajl-devel"
 declare -a epel
 case $osversion in
     rhel-5.*|centos-5.*)
@@ -105,10 +104,12 @@ case $osversion in
     rhel-6.*|centos-6.*)
         epel[0]="--run-command"
         epel[1]="yum install -y --nogpgcheck https://dl.fedoraproject.org/pub/epel/epel-release-latest-6.noarch.rpm"
+        pkgs="$pkgs,jansson-devel"
         ;;
     rhel-7.*|centos-7.*)
         epel[0]="--run-command"
         epel[1]="yum install -y --nogpgcheck https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm"
+        pkgs="$pkgs,jansson-devel"
         ;;
 esac