Wrapper: get rid of bashism, provide better error in some cases

In case the symlink to gtk3-nocsd is the only command present in PATH
with the correct name, instead of just falling back to /bin/false,
pretend to execute /.gtk3-nocsd./$APPNAME - so that the user will get
an error message that might help a little in figuring out what's wrong.

Also, use /bin/sh and not /bin/bash in shebang.

gtk3-nocsd.in

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/bin/sh
 #
 # gtk3-nocsd - Wrapper to apply gtk3-nocsd to application
 #
@@ -72,11 +72,16 @@ fi
 
 # Find the real program (the first one that's not symlinked to get3-nocsd)
 APPNAME="$(basename "$0")"
-for APPPATH in $(type -Pa "$APPNAME") /bin/false; do
+for APPPATH in $(which -a "$APPNAME") /bin/false; do
     APPPATH_LINK="$(readlink -fe "$APPPATH")"
     [ x"${APPPATH_LINK##*/}"x = x"gtk3-nocsd"x ] || break
 done
 
+# Provide error message at all
+if [ x"$APPNAME"x != x"false"x ] && [ x"${APPPATH}"x = x"/bin/false"x ] ; then
+    APPPATH=/.gtk3-nocsd./"$APPNAME"
+fi
+
 # Run the program with CSD disabled
 export LD_PRELOAD="${GTK3_NOCSD}${LD_PRELOAD:+:$LD_PRELOAD}"
 export GTK_CSD=0