academic/grass: Fix some bashisms.

Signed-off-by: dsomero <xgizzmo@slackbuilds.org>

academic/grass/grass.SlackBuild

@@ -70,33 +70,25 @@ find -L . \
  -exec chmod 644 {} \;
 
 # Option handling:
-# $WITHLIST has to be an array due to embedded spaces in the ffmpeg includes :-(
 set -- $(echo $ENABLE | sed 's/,/ /g')
-withnum=0
-while [[ "$1" != "" ]]; do
+
+while [ "$1" != "" ]; do
   case "$1"
   in
   blas | \
   lapack | \
+  ffmpeg | \
   sqlite )
-    WITHLIST[$((withnum++))]="--with-$1"
+    WITHLIST="$WITHLIST --with-$1"
     shift
     ;;
   mysql | mariadb )
-    WITHLIST[$((withnum++))]="--with-mysql"
-    WITHLIST[$((withnum++))]="--with-mysql-includes=/usr/include/mysql"
+    WITHLIST="$WITHLIST --with-mysql"
+    WITHLIST="$WITHLIST --with-mysql-includes=/usr/include/mysql"
     shift
     ;;
   postgres | postgresql )
-    WITHLIST[$((withnum++))]="--with-postgres"
-    shift
-    ;;
-  ffmpeg )
-    FFINCL="/usr/include/libavcodec /usr/include/libavdevice /usr/include/libavfilter \
-            /usr/include/libavformat /usr/include/libavutil /usr/include/libpostproc \
-            /usr/include/libswresample /usr/include/libswscale"
-    WITHLIST[$((withnum++))]="--with-ffmpeg"
-    WITHLIST[$((withnum++))]="--with-ffmpeg-includes=$FFINCL"
+    WITHLIST="$WITHLIST --with-postgres"
     shift
     ;;
   * )
@@ -112,6 +104,8 @@ else
 fi
 
 # geos now always enabled: it's an indirect hard dep (via gdal), and makes grass nicer :-)
+# ffmpeg includes are only parsed if ffmpeg is enabled so it is safe to pass them to configure.
+
 CFLAGS="$SLKCFLAGS" \
 CXXFLAGS="$SLKCFLAGS -fpermissive" \
 LDFLAGS="-ldl -lncurses" \
@@ -128,8 +122,11 @@ LDFLAGS="-ldl -lncurses" \
   --with-wxwidgets \
   --with-geos \
   --enable-largefile  \
-  "${WITHLIST[@]}" \
+  $WITHLIST \
   $BITNESS \
+  --with-ffmpeg-includes="/usr/include/libavcodec /usr/include/libavdevice \
+  /usr/include/libavfilter /usr/include/libavformat /usr/include/libavutil \
+  /usr/include/libpostproc /usr/include/libswresample /usr/include/libswscale" \
   --build=$ARCH-slackware-linux \
   --host=$ARCH-slackware-linux