added feature to check for duplicates when fileing new bugreports

[Markus Korn]

The '+filebug' method of launchpad suggest possible duplicates. It would be nice if py-lp-bugs could addpot this feature.
I started a new branch for this.

Markus

[Markus Korn (thekorn)]

I'm going to merge the changes into the .main branch as soon I've done some more testings. Let me just give you an overviewon how this will work:

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In [16]: from launchpadbugs.connector import ConnectBug

In [17]: B = ConnectBug()

In [18]: B.authentication = "/home/markus/.gnome2/epiphany/mozilla/epiphany/cookies.sqlite"

In [19]: dups1 = B.check_duplicate({"name": "buglog-data"}, "check this for duplicate", "This is an example bugreport to show the features of the new check_duplicate-functionality", tags=["foo"])

In [20]: dups1
Out[20]: [<BugInfo 234363>, <BugInfo 120593>]

In [21]: dups1.submit()
Out[21]: <Bug 234366>

In [22]: _.status
Out[22]: 'New'

In [23]: dups2 = B.check_duplicate({"name": "buglog-data"}, "check this for duplicate", "This is an example bugre
port to show the features of the new check_duplicate-functionality", tags=["foo"])

In [24]: dups2.subscribe(234363)

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Please note:
  * dups.submit() and dups.subscribe(<bugnr>) always returns an LPBugs-object
  * Bug.check_duplicate(<args>) returns a list, members are instances of LPBugInfo
  * dups.subscribe(<bugnr>) seems to be broken in some cases, I've to fix it before merging the changes into the main brach.

Markus