At the moment doit dumpdb always dumps the default database (cf. #126). This makes it hard to debug a a custom dep_file setting. The command should be modified to behave as follows:

• If there is a dodo file (i.e., doit run would run some tasks), then doit dumpdb should dump the database that these tasks would use. This would take into account a modified dep_file in a config file or in a global DOIT_CONFIG dict
• Similarly, in an IPython context, where %doit run would run tasks defined in the current IPython session / notebook, %doit dumpdb should dump the actual database set by a config file or DOIT_CONFIG dict, if available.
• If there is no dodo file, and doit is not run in an IPython context, the default database should be dumped (current behavior)

The above cases handle the situation where no --db-file option is given. It should still be possible to dump as specific database file manually with --db-file.

In all cases, the doit dumpdb command should print the name of the database file it is dumping, just before the database type: in the execute method of DumpDB, adding a line

print("DB file is '%s'" % dep_file)

would suffice. However, making the dumpdb command aware of any defined tasks would be less trivial.