fix cd when user assigns a value to OLDPWD; fix android issue with blocked system calls; fix historical use of test -t; fix issue with foreground-TSTP async jobs

tests/test.right

@@ -279,18 +279,24 @@ b ( 1 = 2
 ./test.tests: line 26: test: (: unary operator expected
 2
 t -t a
-1
+./test.tests: line 26: test: a: integer expected
+2
 t -t addsds
-1
+./test.tests: line 26: test: addsds: integer expected
+2
 t -t 42
 1
 t -t /dev/tty
-1
+./test.tests: line 26: test: /dev/tty: integer expected
+2
 t -t /dev/tty4
-1
+./test.tests: line 26: test: /dev/tty4: integer expected
+2
 t -t /dev/tty4444444...
-1
-1
+./test.tests: line 26: test: /dev/tty4444444...: integer expected
+2
+./test.tests: line 26: test:  : integer expected
+2
 t -p /dev/fd/6
 1
 t -p /dev/fd/6

tests/varenv2.sub

@@ -49,6 +49,10 @@ fff
 x=10 fff
 x=1 fff
 x=4 fff2
+# set this because variable assignments preceding functions should never
+# persist after the function returns, no matter what a builtin inside the
+# function does to them
+x=4
 x=11 fff3
 echo after fff3: x=$x
 x=12 fff4