Don't normalize S3 V4 paths (don't strip trailing / lone ".")

[jamshid]

It's not a common or good S3 key name, but keys like "." and "//.." are valid keys and requests_aws4auth should generate the same signature as AWS S3.

# python
Python 2.7.5 (default, Nov  6 2016, 00:28:07) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-11)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import requests
>>> import requests_aws4auth
>>> AUTH=requests_aws4auth.AWS4Auth('AKIAXXXXXXXXXXFKXWMLQ', '4f6BgjVRgrfKIyk3fkUx4z29EZ9vCzOuVpC/hix8', 'us-east-1', 's3')
>>> r = requests.put('http://mybucket.example.com.s3.amazonaws.com/x/.', data='dot',auth=AUTH)
>>> r.text
u'<?xml version="1.0" encoding="UTF-8"?>\n<Error><Code>SignatureDoesNotMatch</Code><Message>The request signature we calculated does not match the signature you provided. Check your key and signing method.</Message><AWSAccessKeyId>AKIAXXXXXXXXXXKXWMLQ</AWSAccessKeyId><StringToSign>AWS4-HMAC-SHA256\n20170218T062045Z\n20170218/us-east-1/s3/aws4_request\n5700201b57931166eb49924611fbeb117099e7ac79dc7f9a14863bc6df684784</StringToSign><SignatureProvided>6ee791e3f664f9fab411ce7a11ed34b21cfbb827a415e2b1d4a66ac765e42a0d</SignatureProvided><StringToSignBytes>41 57 53 34 2d 48 4d 41 43 2d 53 48 41 32 35 36 0a 32 30 31 37 30 32 31 38 54 30 36 32 30 34 35 5a 0a 32 30 31 37 30 32 31 38 2f 75 73 2d 65 61 73 74 2d 31 2f 73 33 2f 61 77 73 34 5f 72 65 71 75 65 73 74 0a 35 37 30 30 32 30 31 62 35 37 39 33 31 31 36 36 65 62 34 39 39 32 34 36 31 31 66 62 65 62 31 31 37 30 39 39 65 37 61 63 37 39 64 63 37 66 39 61 31 34 38 36 33 62 63 36 64 66 36 38 34 37 38 34</StringToSignBytes><CanonicalRequest>PUT\n/x/.\n\nhost:mahbucke.s3.amazonaws.com\nx-amz-content-sha256:e392dad8b08599f74d4819cd291feef81ab4389e0a6fae2b1286f99411b0c7ca\nx-amz-date:20170218T062045Z\n\nhost;x-amz-content-sha256;x-amz-date\ne392dad8b08599f74d4819cd291feef81ab4389e0a6fae2b1286f99411b0c7ca</CanonicalRequest><CanonicalRequestBytes>50 55 54 0a 2f 78 2f 2e 0a 0a 68 6f 73 74 3a 6d 61 68 62 75 63 6b 65 2e 73 33 2e 61 6d 61 7a 6f 6e 61 77 73 2e 63 6f 6d 0a 78 2d 61 6d 7a 2d 63 6f 6e 74 65 6e 74 2d 73 68 61 32 35 36 3a 65 33 39 32 64 61 64 38 62 30 38 35 39 39 66 37 34 64 34 38 31 39 63 64 32 39 31 66 65 65 66 38 31 61 62 34 33 38 39 65 30 61 36 66 61 65 32 62 31 32 38 36 66 39 39 34 31 31 62 30 63 37 63 61 0a 78 2d 61 6d 7a 2d 64 61 74 65 3a 32 30 31 37 30 32 31 38 54 30 36 32 30 34 35 5a 0a 0a 68 6f 73 74 3b 78 2d 61 6d 7a 2d 63 6f 6e 74 65 6e 74 2d 73 68 61 32 35 36 3b 78 2d 61 6d 7a 2d 64 61 74 65 0a 65 33 39 32 64 61 64 38 62 30 38 35 39 39 66 37 34 64 34 38 31 39 63 64 32 39 31 66 65 65 66 38 31 61 62 34 33 38 39 65 30 61 36 66 61 65 32 62 31 32 38 36 66 39 39 34 31 31 62 30 63 37 63 61</CanonicalRequestBytes><RequestId>82D0203691B42F72</RequestId><HostId>+hs490EpTExGxdiLIodEzBDi+M7pcN9Ib+xGrI6bhrr4Qb0a6WzrVsqtJewvS+f80RxCTt0xl5Y=</HostId></Error>'

This fix seems to be simple, just remove posixpath.normpath() (which removes trailing / embedded dot and dot-dot), and stop removing duplicate "/".

But I guess that was added for a reason?

diff -u /usr/lib/python2.7/site-packages/requests_aws4auth/aws4auth.py~ /usr/lib/python2.7/site-packages/requests_aws4auth/aws4auth.py
--- /usr/lib/python2.7/site-packages/requests_aws4auth/aws4auth.py~	2017-02-15 19:17:02.000000000 +0000
+++ /usr/lib/python2.7/site-packages/requests_aws4auth/aws4auth.py	2017-02-18 00:18:15.425646504 +0000
@@ -288,7 +288,7 @@
                                    self.signing_key.secret_key is None):
             raise NoSecretKeyError
 
-        secret_key = secret_key or self.signing_key.secret_key
+        secret_key = secret_key or (self.signing_key and self.signing_key.secret_key) or ''
         region = region or self.region
         service = service or self.service
         date = date or self.date
@@ -604,7 +604,7 @@
         if '?' in fixed_path:
             fixed_path, qs = fixed_path.split('?', 1)
-        fixed_path = posixpath.normpath(fixed_path)
+#        fixed_path = posixpath.normpath(fixed_path)
-        fixed_path = re.sub('/+', '/', fixed_path)
+#        fixed_path = re.sub('/+', '/', fixed_path)
         if path.endswith('/') and not fixed_path.endswith('/'):
             fixed_path += '/'
         full_path = fixed_path