Add a --sysinfo flag to all daemons

This dumps all the platform information and mitmproxy version data we'd
normally need to troubleshoot an issue.

netlib/debug.py

@@ -0,0 +1,26 @@
+import platform
+from netlib import version
+
+"""
+    Some utilities to help with debugging.
+"""
+
+def sysinfo():
+    data = [
+        "Mitmproxy verison: %s"%version.VERSION,
+        "Python version: %s"%platform.python_version(),
+        "Platform: %s"%platform.platform(),
+    ]
+    d = platform.linux_distribution()
+    if d[0]:
+        data.append("Linux distro: %s %s %s"%d)
+
+    d = platform.mac_ver()
+    if d[0]:
+        data.append("Mac version: %s %s %s"%d)
+
+    d = platform.win32_ver()
+    if d[0]:
+        data.append("Windows version: %s %s %s %s"%d)
+
+    return "\n".join(data)