bundler -- this could be a real install wrapper

[Fred T. Hamster]

real installer wrapper:

1. features of graphical installers, wrapping bundler as the storage mechanism.
2. query for target directory automatically: (installer-like feature)
   1. ask the user if the target dir is not set?
   2. do a graphical thing for win32 and x windows, and a text thing if DISPLAY not set on linux or console mode on win32.
   3. follow bundler tradition... add a new attribute for this. "query if not set"
   4. and another attribute for how to handle the query? abort if not specified.
   5. ask until they hit cancel or provide non-empty answer.