Fix segfault if $PATH contains a .paths directory (#55)

ksh crashed if it encountered a .paths directory in any of the
directories in $PATH.

Ref: 1534855

src/cmd/ksh93/sh/path.c: path_chkpaths():
- Refuse to read .paths if it's not a regular file
  or a symlink to a regular file.

src/cmd/ksh93/tests/path.sh

@@ -408,6 +408,15 @@ END
 v=$(PATH=/dev/null "$SHELL" -c 'command -p ls /dev/null')
 [[ $v == /dev/null ]] || err_exit 'command -p fails to find standard utility'
 
+# ksh segfaults if $PATH contains a .paths directory
+mkdir -p $tmp/paths-dir-crash/
+cat > $tmp/paths-dir-crash/run.sh <<- EOF
+mkdir -p $tmp/paths-dir-crash/.paths
+export PATH=$tmp/paths-dir-crash:$PATH
+print ok
+EOF
+[[ $($SHELL $tmp/paths-dir-crash/run.sh 2>/dev/null) == ok ]] || err_exit "ksh crashes if PATH contains a .paths directory"
+
 # ======
 exit $((Errors<125?Errors:125))