Replace sys.exc_type with sys.exc_info.

[alexandrevicenzi]

sys.exc_type has been removed in Python 3 and the same behavior was mantained with sys.exc_info logic.

This fixes #124.

[coveralls]

Pull Request Test Coverage Report for Build 156

• 0 of 2 (0.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.02%) to 53.292%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
kobo/django/xmlrpc/dispatcher.py	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
kobo/django/xmlrpc/dispatcher.py	1	0.0%

Totals
Change from base Build 149:	-0.02%
Covered Lines:	3173
Relevant Lines:	5954

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💛 - Coveralls