global: use raw strings for regular expressions with escapes Escape sequences like \w, \s, and \d are technically invalid in str/bytes. This became a deprecation warning in Python 3.6 (https://bugs.python.org/issue27364). Python 3.8 bumps it to a SyntaxWarning (https://bugs.python.org/issue32912), which is non-silent by default. This commit changes a number of regular expressions to use br'' so regular expression special sequences don't need \\ literals. This fixes roughly half of the SyntaxWarning we see in the code base with Python 3.8. Differential Revision: https://phab.mercurial-scm.org/D5815