tests: introduce 'seq.py' as a portable replacement for 'seq'

OS X 10.6.8 doesn't have it, while 10.10 does.  I'm not sure when it was added.
It may be missing from other platforms as well.

This currently doesn't handle the string manipulation options (-f, -s and -w in
MinGW anyway), since there is currently no need for it.  Since xrange defaults
to starting at 0 instead of 1, and treats the end as exclusive instead of
inclusive, the args need to be extracted instead of doing:

        xrange(*[int(a) for a in sys.argv[1:]])

Therefore, the step might as well be added, even though there is no current use.

tests/seq.py

@@ -0,0 +1,23 b''
+#!/usr/bin/env python
+#
+# A portable replacement for 'seq'
+#
+# Usage:
+#   seq STOP              [1, STOP] stepping by 1
+#   seq START STOP        [START, STOP] stepping by 1
+#   seq START STEP STOP   [START, STOP] stepping by STEP
+
+import sys
+
+start = 1
+if len(sys.argv) > 2:
+    start = int(sys.argv[1])
+
+step = 1
+if len(sys.argv) > 3:
+    step = int(sys.argv[2])
+
+stop = int(sys.argv[-1]) + 1
+
+for i in xrange(start, stop, step):
+    print i