Adds generic SoftLayer request object

This allows both transports to (mostly) use this one object to define the
specifications of an API call.
Removes ability to specify which rest file extension to use
Fixes user-metadata bug/clearifies debugging output
Don't set headers to None when they're empty
Proxies missing a protocol raises differently in py2.6 + misc changes
Clarifies doc blocks
Fixes small style issue
Merge branch 'master' of github.com:softlayer/softlayer-python into auth-revisit
Merge pull request #396 from sudorandom/auth-revisit

Auth revisit