Arg, forgot the most important:
Put the pandoc version test under the pandoc_available test.
This avoids raising an exception when the module is imported:
the exception is only raised on pandoc(...) function calls.

It also prints warnings if pandoc is not found at import time
and if the version does not meet the expected one.
Fix exception handler syntax for Python 3 compatibility.
Improve error messages.
Merge branch 'minimal-pandoc' into mystaging