DSK, .profile: Update, more robust PATH patching

.profile

@@ -33,7 +33,11 @@ else
 	export EDITOR="vi"
 fi
 
-export PATH=$PATH:$HOME/.local/bin
+# Patch PATH if necessary
+# This string substitution is POSIX-compliant
+localbindir="$HOME/.local/bin"
+[ "${PATH#*$localbindir}" == "$PATH" ] && export PATH="$PATH:$localbindir"
+unset localbindir
 
 # If emerge exists, add emerge aliases
 if `which emerge > /dev/null 2>&1` ; then