Added code to move old octoprint folder out of the way

Might be left over after an update due to contained .pyc files that then cause the actual application start-up to fail.

run

@@ -6,11 +6,25 @@ print """
 !!! Please perform 'sudo python setup.py install' and  !!!
 !!! use the 'octoprint' executable instead.            !!!
 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
-
 """
 
+import os
 import sys
-sys.path.append("src")
+
+basedir = os.path.dirname(os.path.realpath(__file__))
+
+old = os.path.join(basedir, "octoprint")
+if os.path.exists(old):
+    # rename left-overs from old file structure
+    print """
+Found left-overs from old file structure, renaming to
+"octoprint.backup". Please remove this manually (I don't
+dare to do so myself since you might have changes in there
+I don't know anything about).
+"""
+    os.rename(old, os.path.join(basedir, "octoprint.backup"))
+
+sys.path.append(os.path.join(basedir, "src"))
 
 import octoprint
 octoprint.main()