tests/check-gendoc

py3: conditionalize the raise statement

raise E,V,T is not acceptable in Python 3, thats is conditionalized.
Moreover this will result in syntax error so we have to use exec() to
execute this. Related PEP- https://www.python.org/dev/peps/pep-3109/#id14

My implementation is motivated from the six implementation except they are
defining a new function exec_() to prevent adding an extra frame AFAIK :)

https://bitbucket.org/gutworth/six/src/ca4580a5a648/six.py#six.py-680

#!/bin/sh
HGENCODING=UTF-8
export HGENCODING

echo ".. -*- coding: utf-8 -*-" > gendoc.txt
echo "" >> gendoc.txt
LANGUAGE=$1 python "$TESTDIR/../doc/gendoc.py" >> gendoc.txt 2> /dev/null || exit

echo "checking for parse errors"
python "$TESTDIR/../doc/docchecker" gendoc.txt
python "$TESTDIR/../doc/runrst" html gendoc.txt /dev/null