#27364: fix "incorrect" uses of escape character in the stdlib.

And most of the tools.

Patch by Emanual Barry, reviewed by me, Serhiy Storchaka, and
Martin Panter.
diff --git a/Tools/unicode/gencodec.py b/Tools/unicode/gencodec.py
index 4c21469..31f0112 100644
--- a/Tools/unicode/gencodec.py
+++ b/Tools/unicode/gencodec.py
@@ -37,11 +37,11 @@
 # Placeholder for a missing code point
 MISSING_CODE = -1
 
-mapRE = re.compile('((?:0x[0-9a-fA-F]+\+?)+)'
-                   '\s+'
-                   '((?:(?:0x[0-9a-fA-Z]+|<[A-Za-z]+>)\+?)*)'
-                   '\s*'
-                   '(#.+)?')
+mapRE = re.compile(r'((?:0x[0-9a-fA-F]+\+?)+)'
+                   r'\s+'
+                   r'((?:(?:0x[0-9a-fA-Z]+|<[A-Za-z]+>)\+?)*)'
+                   r'\s*'
+                   r'(#.+)?')
 
 def parsecodes(codes, len=len, range=range):