fix sorting of categories list
fix sorting of authors list
remove unittest.skip statements for functional tests
update custom output now that categories are correctly sorted

pelican -o tests/output/custom/ -s samples/pelican.conf.py samples/content/
update basic output now that categories are correctly sorted

pelican -o tests/output/basic/ samples/content/
mock getenv to always return the same value for $USER
update basic output with $USER="Dummy Author"

USER="Dummy Author" pelican -o tests/output/basic/ samples/content/
add instructions to regenerate the output of functional tests
fix command to regenerate the output of basic functional test

the command needs to be prefixed by USER="Dummy Author" which is the author
name value mocked in the corresponding functional test.
Merge branch 'master' of https://github.com/ametaireau/pelican into fix-sort-categories
test that categories are ordered as expected
Merge branch 'fix-sort-categories' into fix-functional-tests
Merge branch 'master' into fix-functional-tests

Conflicts:
	tests/test_generators.py
update functional tests output
be more verbose when functional tests fail
clean up temporary dirs in tearDown to force cleanup even if tests fail
Merge branch 'master' of https://github.com/ametaireau/pelican into fix-functional-tests
force locale to ascii in functional tests
update command to generate functional tests output

we need to force LC_ALL="C" to avoid generating articles/pages in other
languages
replace FALLBACK_ON_FS_DATE by DEFAULT_DATE

DEFAULT_DATE allows to specify any default date as a tuple in addition to the
fallback on filesystem mtime check