cleanRequestData modifies arguments causing a set call to not work as required

[GoogleCodeExporter]

What steps will reproduce the problem?
1. Call the set function with multiple "files-wanted" values, such as 
$arguments[ 'files-wanted' ] = array( 0,1,2,3,4 );
2. Dump the evaluated value of "json_encode( $arguments );" before the call to 
cleanRequestData in the request function, and again afterwards to see the 
effect its having. 

File Id 0 ends up being dropped from the arguments, whilst all other numbers 
now have an associated key, which Transmission doesn't seem to like and ignores 
all values.  Also makes File Id 0 impossible to set.

What is the expected output? What do you see instead?
I expect: "files-wanted":[0,1,2,3,4]
I get   : "files-wanted":{"1":1,"2":2,"3":3,"4":4}

What version of the product are you using? On what operating system?
v0.3, Windows 7, PHP v5.2.17


Please provide any additional information below.

Its the same with a set request for "files-unwanted".
Single Ids on their own aren't affected, except for specifying an Id of 0, 
which as a result of being stripped out leaves the id list empty and as per the 
spec, means all files will be marked as wanted/unwanted instead.
Commenting out the call to cleanRequestData gets the result I expect, but 
breaks other functionality.

Original issue reported on code.google.com by chrismar...@gmail.com on 27 May 2011 at 2:04