- reworked the plugin loading mechanism

Using the "old" exec approach isn't possible anymore because it'll break all
plugins which aren't compatible with python3 (for instance the usage of
python2's "print" statement will lead to an error). In order to circumvent
this problem we do the following:

- import the plugin/module
- update the module's global symbol table with the "globals()" of the
  commandline module
- bind the module's "do_*" functions to the "Osc" class

This basically mimics the old "exec" semantics.

osc/commandline.py

@@ -10,6 +10,8 @@ from . import conf
 from . import oscerr
 import sys
 import time
+import imp
+import inspect
 try:
     from urllib.parse import urlsplit
     from urllib.error import HTTPError
@@ -75,6 +77,9 @@ class Osc(cmdln.Cmdln):
     man_footer = MAN_FOOTER
 
     def __init__(self, *args, **kwargs):
+        # the plugins have to be loaded before the
+        # superclass' __init__ method is called
+        self._load_plugins()
         cmdln.Cmdln.__init__(self, *args, **kwargs)
         cmdln.Cmdln.do_help.aliases.append('h')
         sys.stderr = safewriter.SafeWriter(sys.stderr)
@@ -7900,22 +7905,28 @@ Please submit there instead, or use --nodevelproject to force direct submission.
                 print('done. Please check the state of the wc (via \'osc status %s\').' % i)
             else:
                 print('osc: working copy \'%s\' is not inconsistent' % i, file=sys.stderr)
-# fini!
-###############################################################################
 
-    # load subcommands plugged-in locally
+    def _load_plugins(self):
         plugin_dirs = [
             '/usr/lib/osc-plugins',
             '/usr/local/lib/osc-plugins',
             '/var/lib/osc-plugins',  # Kept for backward compatibility
             os.path.expanduser('~/.osc-plugins')]
         for plugin_dir in plugin_dirs:
-        if os.path.isdir(plugin_dir):
+            if not os.path.isdir(plugin_dir):
+                continue
             for extfile in os.listdir(plugin_dir):
                 if not extfile.endswith('.py'):
                     continue
                 try:
-                    exec(open(os.path.join(plugin_dir, extfile)).read())
+                    modname = os.path.splitext(extfile)[0]
+                    mod = imp.load_source(modname, os.path.join(plugin_dir, extfile))
+                    # restore the old exec semantic
+                    mod.__dict__.update(globals())
+                    for name in dir(mod):
+                        func = getattr(mod, name)
+                        if name.startswith('do_') and inspect.isfunction(func):
+                            setattr(self.__class__, name, func)
                 except SyntaxError as e:
                     if (os.environ.get('OSC_PLUGIN_FAIL_IGNORE')):
                         print("%s: %s\n" % (os.path.join(plugin_dir, extfile), e), file=sys.stderr)
@@ -7926,5 +7937,7 @@ Please submit there instead, or use --nodevelproject to force direct submission.
                         print("\n Try 'env OSC_PLUGIN_FAIL_IGNORE=1 osc ...'", file=sys.stderr)
                         sys.exit(1)
 
+# fini!
+###############################################################################
 
 # vim: sw=4 et