[Buildbot] #3437: format configuration file syntax errors in more friendly way

[Buildbot trac]

#3437: format configuration file syntax errors in more friendly way
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Reporter:  rutsky     |       Owner:
    Type:  undecided  |      Status:  new
Priority:  major      |   Milestone:  undecided
 Version:  0.9.0b6    |  Resolution:
Keywords:             |
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Comment (by rutsky):

 Provided above changes verbosely handle non-ConfigErrors exceptions that
 is thrown when config file is executed, there may be only single exception
 per configuration, so only single stack trace will be shown.

 In the example above two stack traces of the same exceptions are
 displayed: Python's native exception, that is relative to call site (e.g.
 just above of `master.cfg`), and Twisted's exception that shows place
 where file parsing occurred relative to whole Buildbot master process (IMO
 Twisted exception should include "rethrowed" Python exception, but it
 doesn't).

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Ticket URL: <http://trac.buildbot.net/ticket/3437#comment:2>
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