Allow overriding pycdio dependency

Keep in mind overriding isn’t the suggested behavior.

README.md

@@ -52,10 +52,10 @@ REQUIREMENTS
 - GStreamer and its python bindings, for encoding
   - gstreamer0.10-base-plugins >= 0.10.22 for appsink
   - gstreamer0.10-good-plugins for wav encoding (it depends on the Linux distro used)
-- python musicbrainz2, for metadata lookup
+- python musicbrainzngs, for metadata lookup
 - python-setuptools, for plugin support
 - python-cddb, for showing but not using disc info if not in MusicBrainz
-- pycdio, for drive identification (optional)
+- pycdio, for drive identification (it can be overridden placing a blank file named `PYCDIO_IGNORE` into whipper's config path)
   - Required for drive offset and caching behavior to be stored in the config file
 
 Additionally, if you're building from a git checkout:

morituri/rip/cd.py

@@ -30,7 +30,7 @@ import gobject
 gobject.threads_init()
 
 from morituri.common import logcommand, common, accurip, gstreamer
-from morituri.common import drive, program, task
+from morituri.common import drive, program, task, directory
 from morituri.result import result
 from morituri.program import cdrdao, cdparanoia
 from morituri.rip import common as rcommon
@@ -168,9 +168,20 @@ class _CD(logcommand.LogCommand):
                 self.program.result.release = \
                 cdio.Device(self.device).get_hwinfo()
         except ImportError:
-            raise ImportError("Pycdio module import failed.\n"
-                              "This is a hard dependency: if not available "
-                              "please install it")
+            d = directory.Directory()
+            path = os.path.dirname(d.getConfig())
+            fullPath = os.path.join(path, 'PYCDIO_IGNORE')
+            if os.path.isfile(fullPath):
+                self.stdout.write(
+                    'WARNING: pycdio not installed, cannot identify drive '
+                    '(hard dependency overridden)\n')
+                self.program.result.vendor = 'Unknown'
+                self.program.result.model = 'Unknown'
+                self.program.result.release = 'Unknown'
+            else:
+                raise ImportError("Pycdio module import failed.\n"
+                                  "This is a hard dependency: if not "
+                                  "available please install it")
 
         self.doCommand()