Fixed a typo with encoding parsing

Seems like a typo with encoding parsing. Fixed.
Got rid of to_link_header and changed isEqual

`to_link_header` not needed as the http transport has its own function
for that.

`isEqual` is inconsistent with changes so far.
Removed get_key, get_tag, get_bucket for RiakLink

Replaced the methods with just direct access to the attributes.
Same typo in PBC client as well
Merge pull request #196 from shuhaowu/encoding-typo

Fixed a typo with encoding parsing
Merge pull request #197 from shuhaowu/link-improvements

Link improvements
Re-add exports to the top-level. Closes #193.
Add RiakLink to top-level exports and fix pep8 problems.
Fix pyflakes warning in util.py about redefinition of 'getter' method.
Merge pull request #198 from basho/sdc-export-toplevels

Re-add exports to the top-level. Closes #193.
Use UserWarning since this is not Python stdlib code.
Merge pull request #199 from basho/sdc-fix-redef-warning

Fix pyflakes warning in util.py about redefinition of 'getter' method.
Don't silently drop the port option, instead use it for the default protocol port. Closes #194.
Merge pull request #194 from basho/gh194-port-deprecation

port argument to RiakClient is "silently" ignored
add bucket property clearing.
updates for comments.
Merge pull request #200 from basho/pevm-clear-props

Allow clearing of bucket properties.