Add the trimmed option to the blocktrans tag to trim any newlines and
whitespace from its content.
This allows the developer to indent the blocktrans tag without adding
new lines and whitespace to the msgid in the PO file.
Thanks to mpessas for the initial patch and Dmitri Fedortchenko for the
report.
This shows itself with Python 3 under Windows where UTF-8 usually isn't
the default file I/O encoding and caused one failure and three errors
in our test suite under that platform setup.
Literals from source files with Django template language syntax don't
have a '.py' suffix anymore.
Also, the '.\' prefix is preserved to respect GNU gettext behavior on
that platform.
Refs #16903.
Fixes#19584.
This implies stop storing file path command line arguments in envvars as
a security measure to start relying on with Popen's shell=False instead,
and addition of an 'utils' module.
Thanks kmichel_wgs for the report.