s4cmd: avoid AttributeError on newer botocore

Newer botocore has removed `vendored` entirely; try to import carefully.
Makes s4cmd work again on botocore-1.29.84.

```
Traceback (most recent call last):
  File "/usr/lib/python-exec/python3.10/s4cmd", line 33, in <module>
    sys.exit(load_entry_point('s4cmd==2.1.0', 'console_scripts', 's4cmd')())
  File "/usr/lib/python-exec/python3.10/s4cmd", line 25, in importlib_load_entry_point
    return next(matches).load()
  File "/usr/lib/python3.10/importlib/metadata/__init__.py", line 171, in load
    module = import_module(match.group('module'))
  File "/usr/lib/python3.10/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1050, in _gcd_import
  File "<frozen importlib._bootstrap>", line 1027, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1006, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 688, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 883, in exec_module
  File "<frozen importlib._bootstrap>", line 241, in _call_with_frames_removed
  File "/usr/lib64/python-exec/python3.10/s4cmd.py", line 255, in <module>
    class BotoClient(object):
  File "/usr/lib64/python-exec/python3.10/s4cmd.py", line 274, in BotoClient
    botocore.vendored.requests.packages.urllib3.exceptions.ReadTimeoutError,
AttributeError: module 'botocore' has no attribute 'vendored'
```

Signed-off-by: Robin H. Johnson <[email protected]>

s4cmd.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/python3.10
 
 #
 # Copyright 2012-2018 BloomReach, Inc.
@@ -60,8 +60,8 @@ def cmp(a, b):
 TEMP_FILES = set()
 
 # Environment variable names for S3 credentials.
-S3_ACCESS_KEY_NAME = "AWS_ACCESS_KEY_ID"
-S3_SECRET_KEY_NAME = "AWS_SECRET_ACCESS_KEY"
+S3_ACCESS_KEY_NAME = "S3_ACCESS_KEY"
+S3_SECRET_KEY_NAME = "S3_SECRET_KEY"
 S4CMD_ENV_KEY = "S4CMD_OPTS"
 
 
@@ -271,9 +271,13 @@ class BotoClient(object):
   S3RetryableErrors = (
     socket.timeout,
     socket.error if IS_PYTHON2 else ConnectionError,
-    botocore.vendored.requests.packages.urllib3.exceptions.ReadTimeoutError,
     botocore.exceptions.IncompleteReadError
   )
+  try:
+      # Newer boto removed botocore.vendored entirely.
+      S3RetryableErrors += (botocore.vendored.requests.packages.urllib3.exceptions.ReadTimeoutError,)
+  except AttributeError:
+      pass
 
   # List of API functions we use in s4cmd.
   ALLOWED_CLIENT_METHODS = [
@@ -655,7 +659,7 @@ def s3_keys_from_s3cfg(opt):
       config = ConfigParser.ConfigParser()
       config.read(s3cfg_path)
       keys = config.get("default", "access_key"), config.get("default", "secret_key")
-      debug("read S3 keys from %s file", s3cfg_path)
+      debug("read S3 keys from $HOME/.s3cfg file")
       return keys
     except Exception as e:
       info("could not read S3 keys from %s file; skipping (%s)", s3cfg_path, e)
@@ -1158,7 +1162,7 @@ def partial_match(self, path, filter_path):
     fi = filter_path.split(PATH_SEP)
 
     # Here, if we are in recursive mode, we allow the pi to be longer than fi.
-    # Otherwise, length of pi should be equal or less than the length of fi.
+    # Otherwise, length of pi should be equal or less than the lenght of fi.
     min_len = min(len(pi), len(fi))
     matched = fnmatch.fnmatch(PATH_SEP.join(pi[0:min_len]), PATH_SEP.join(fi[0:min_len]))
     return matched and (self.opt.recursive or len(pi) <= len(fi))