N streams by making the stream a vector of stream shared pointers
that is protected by a mutex. Streams can be get/set by index which
allows indexes to be defined as stream indentifiers. If a stream is
set at index 3 and there are now streams in the collection, then
empty stream objects are inserted to ensure that stream at index 3
has a valid stream. There is also an append method that allows a stream
to be pushed onto the stack. This will allow our streams to be very
flexible in where the output goes.

Modified the CommandReturnObject to use the new StreamTee functionality.
This class now defines two StreamTee indexes: 0 for the stream string
stream, and 1 for the immediate stream. This is used both on the output
and error streams.

Added the ability to get argument types as strings or as descriptions.
This is exported through the SBCommandInterpreter API to allow external
access.

Modified the Driver class to use the newly exported argument names from
SBCommandInterpreter::GetArgumentTypeAsCString().

llvm-svn: 126067