B2X support, locktime-based coin splitting utility

- full support for B2X fork
- `mmgen-split` coin splitting utility for replayable forks
- `mmgen-regtest fork` command for testing forking scenarios
- `regtest_split` command added to `test/test.py` test suite
- timelock support for `txcreate` and `txdo`
- nlocktime and nsequence checks after signing and before sending

cmds/mmgen-autosign

@@ -312,6 +312,7 @@ def set_led(cmd):
 	led_thread.start()
 
 def get_insert_status():
+	if os.getenv('MMGEN_TEST_SUITE'): return True
 	try: os.stat(os.path.join('/dev/disk/by-label/',part_label))
 	except: return False
 	else: return True

cmds/mmgen-split

@@ -0,0 +1,24 @@
+#!/usr/bin/env python
+
+# mmgen = Multi-Mode GENerator, command-line Bitcoin cold storage solution
+# Copyright (C)2013-2017 Philemon <mmgen-py@yandex.com>
+#
+# This program is free software: you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free Software
+# Foundation, either version 3 of the License, or (at your option) any later
+# version.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE.  See the GNU General Public License for more
+# details.
+#
+# You should have received a copy of the GNU General Public License along with
+# this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""
+mmgen-split: Split funds after a fork using a timelocked transaction
+"""
+
+from mmgen.main import launch
+launch("split")