Fix migration planner to fully understand squashed migrations. And test.
Fixed #19941 -- Removed sys.path hack when running the test suite.

Thanks jezdez for the suggestion.
Bumped release date for 1.5.5 & 1.4.9.
Fixed #20945 -- Allowed cache tag to use a specific cache.
Added missing newline in docstring; refs #20945.
Start attacking E231 violations
Fixed #21299 - Changed filters from title to capfirst on admin inline formsets.

Previously there was a mixture of the two which resulted in inconsistent
casing.
Fixed #21227 -- Added workaround for selenium test failures

Added a refresh() before quit() in the selenium tests, since this
solves the problem of spurious test failures in some environments.
Fixed #20338 -- Stripped ending dot during host validation

Thanks manfre for the report and Timo Graham for the review.
Fixed #21219 -- Added a way to set different permission for static files.

Previously, when collecting static files, the files would receive permission
from FILE_UPLOAD_PERMISSIONS. Now, there's an option to give different
permission from uploaded files permission by subclassing any of the static
files storage classes and setting the file_permissions_mode parameter.

Thanks dblack at atlassian.com for the suggestion.
Fixed #21271 -- Added timeout parameter to SMTP EmailBackend.

Thanks Tobias McNulty and Tim Graham for discussions and code review.
Thanks Andre Cruz the suggestion and initial patch.
Fixed doc typo in previous commit.