deprecate Base64 - use commons-codec in 2.1

[Jeffrey Dever <js...@sympatico.ca>]

The Commons Codec project (currently in the sandbox) is taking the 
responsibility for maintaining the Base64 class that is in common use in 
Jakarta.

They initially took the code from the httpclient package (including the 
associated tests), and have merged some changes that were made by the 
xml-rpc project, which was also based on the Base64 in httpclient (which 
was in turn based on a version in Slide).

I propose we take steps to support the commons-codec project by using 
them as the authoritative source for Base64 in HttpClient.

As the Base64 class in HttpClient is public, should deprecate the 
HttpClient Base64 class now, but not remove it untill 2.1 to give users 
time to adjust.  We will also have to add codec as a runtime dependancy, 
which should also be done in 2.1 to maintain stability for the current 
work on 2.0.  This will also give some time for codec to be promoted out 
of the sandbox.

Jandalf.