drawdag: use raw strings for docstrings
Avoids SyntaxWarning for invalid \ escape on Python 3.8.
Differential Revision: https://phab.mercurial-scm.org/D5827
check-config: use raw strings for regular expressions
This avoids SyntaxWarning on Python 3.8 for invalid \ escapes.
Differential Revision: https://phab.mercurial-scm.org/D5826