graphics/mtpaint: Miscellaneous cleanups (remove bashisms)

Signed-off-by: Robby Workman <rworkman@slackbuilds.org>

graphics/mtpaint/mtpaint.SlackBuild

@@ -6,15 +6,13 @@
 
 PRGNAM=mtpaint
 VERSION=${VERSION:-3.31}
-BUILD=${BUILD:-1}
+BUILD=${BUILD:-2}
 TAG=${TAG:-_SBo}
 
-# Automatically determine the architecture we're building on:
 if [ -z "$ARCH" ]; then
   case "$( uname -m )" in
     i?86) ARCH=i486 ;;
     arm*) ARCH=arm ;;
-    # Unless $ARCH is already set, use uname -m for all other archs:
        *) ARCH=$( uname -m ) ;;
   esac
 fi
@@ -38,13 +36,13 @@ else
   LIBDIRSUFFIX=""
 fi
 
-if [[ $GTK1 == yes ]]; then
+if [ "$GTK1" = yes ]; then
     GTK1=gtk1
 fi
-if [[ $TKWIDGETS == yes ]]; then
+if [ "$TKWIDGETS" = yes ]; then
     TKWIDGETS="gtkfilesel gtkcolsel"
 fi
-if [[ $INTL == yes ]]; then
+if [ "$INTL" = yes ]; then
     INTL=intl
 fi
 
@@ -85,7 +83,7 @@ for i in $( find $PKG/usr/man -type l ) ; do ln -s $( readlink $i ).gz $i.gz ; r
 # go ahead and make this in case the handbook is skipped
 mkdir -p $PKG/usr/doc/$PRGNAM-$VERSION
 
-if [[ $HANDBOOK == yes ]]; then
+if [ $HANDBOOK = yes ]; then
     unzip $CWD/${PRGNAM}_handbook-$VERSION.zip
     cd ${PRGNAM}_handbook-$VERSION
     chown -R root:root .