Unset CDPATH if it is set.

Apparently on some (probably buggy) platforms, when CDPATH is set, the
'cd' command will always print text to stdout.  This caused fail 122
and 123 in shelltest.od.

CDPATH is an interactive-mode option, so let's clear it when running
scripts.

minimal/do

@@ -17,6 +17,9 @@ usage: do [-d] [-x] [-v] [-c] <targets...>
   It will never rebuild a target it has already built, unless you use -c.
 "
 
+# CDPATH apparently causes unexpected 'cd' output on some platforms.
+unset CDPATH
+
 # By default, no output coloring.
 green=""
 bold=""

redo/builder.py

@@ -309,6 +309,8 @@ class _BuildJob(object):
         # now.
         assert state.is_flushed()
         newp = os.path.realpath(dodir)
+        # CDPATH apparently caused unexpected 'cd' output on some platforms.
+        os.unsetenv('CDPATH')
         os.environ['REDO_PWD'] = state.relpath(newp, env.v.STARTDIR)
         os.environ['REDO_TARGET'] = basename + ext
         os.environ['REDO_DEPTH'] = env.v.DEPTH + '  '

t/shelltest.od

@@ -513,7 +513,7 @@ x=$(printf "a%-5sc" "b")
 [ "$x" = "ab    c" ] || warn 119
 
 # Make sure cd supports -L and -P options properly
-rm -f shlink
+rm -f shlink ../shlink
 ln -s . shlink
 (quiet_stderr cd -L shlink/shlink/shlink/../shlink) || fail 120
 (quiet_stderr cd -P shlink/shlink/shlink/../shlink) && fail 121