Jira: https://issues.apache.org/jira/browse/SPARK-8235

I added the support for sha1. If I understood rxin correctly, sha and sha1 should execute the same algorithm, shouldn't they?

Please take a close look on the Python part. This is adopted from #6934

Author: Tarek Auel <tarek.auel@gmail.com>
Author: Tarek Auel <tarek.auel@googlemail.com>

Closes #6963 from tarekauel/SPARK-8235 and squashes the following commits:

f064563 [Tarek Auel] change to shaHex
7ce3cdc [Tarek Auel] rely on automatic cast
a1251d6 [Tarek Auel] Merge remote-tracking branch 'upstream/master' into SPARK-8235
68eb043 [Tarek Auel] added docstring
be5aff1 [Tarek Auel] improved error message
7336c96 [Tarek Auel] added type check
cf23a80 [Tarek Auel] simplified example
ebf75ef [Tarek Auel] [SPARK-8301] updated the python documentation. Removed sha in python and scala
6d6ff0d [Tarek Auel] [SPARK-8233] added docstring
ea191a9 [Tarek Auel] [SPARK-8233] fixed signatureof python function. Added expected type to misc
e3fd7c3 [Tarek Auel] SPARK[8235] added sha to the list of __all__
e5dad4e [Tarek Auel] SPARK[8235] sha / sha1