Add the git_checkout rule

It creates a branch before checking-out to it if the branch does not
exist.

thefuck/rules/git_checkout.py

@@ -0,0 +1,15 @@
+import re
+
+
+def match(command, settings):
+    return ('git' in command.script
+            and 'did not match any file(s) known to git.' in command.stderr
+            and "Did you forget to 'git add'?" not in command.stderr)
+
+
+def get_new_command(command, settings):
+    missing_file = re.findall(
+            r"error: pathspec '([^']*)' "
+            "did not match any file\(s\) known to git.", command.stderr)[0]
+
+    return 'git branch {} && {}'.format(missing_file, command.script)