Run tests in parallel or only some with a filter

`make check JOBS=4` will spawn 4 workers and spread the tests among them.
`make check FILTER=try` will only run tests that contain `try` in their name.

tests/all_tests.sh

@@ -1,13 +1,10 @@
 #!/bin/bash
+set -e
 
 srcdir="$(cd "$(dirname "${BASH_SOURCE[0]}")"/.. && pwd)"
+jobs=${JOBS:-4}
+filter=${FILTER:-""}
 
-test_status=0
-test_files=( "$srcdir"/tests/tokenized/*.txt )
-for tf in "${test_files[@]}"; do
-    test_name="$(basename "$tf")"
-    test_name="${test_name%.txt}"
-    "$srcdir"/tests/decompyle_test.sh $test_name tests || test_status=1
-done
-
-exit $test_status
+find "${srcdir}/tests/tokenized" -type f -name '*.txt' -a -name "*${filter}*" -print0 | \
+    xargs -0 -I '{}' -P $jobs \
+          bash -c 'o=$('"$srcdir"'/tests/decompyle_test.sh "$(basename -s .txt "{}")" tests-out) r=$?; echo "$o"; exit $r'