Automatically split the request for package info into URI lengths les

[AerysL]

…s than 8125 chars

Divides the request into requests at most 8000 characters long, allowing the request to be successful.
Modifies the DownloadJson() function of pacaur.

Potentially addresses #209,#238 , #504

~~ Do note that while this fixes the bug in pacaur, it appears that the YAJL tools (json_verify, json_reformat) have a maximum allowed json character limit of 2^18=262144, and so if the rpc return is larger than this limit, json_verify and json_reformat fail causing pacaur to fail. Although as I have not communicated with the devs it is possible that I just happen to have errors around that location in the files I test. Due to this I cannot completely test the pacaur to successful completion, however in my tests this fixed DownloadJson(). ~~

It appears that my error was caused by the use of sed, and was fixed by running sed twice.

[rmarquis]

Thanks for this PR.

Can you give an example of why sed is required twice? I won't merge code that I don't understand the purpose.

Don't have time to look in details at this PR yet, but will probably do tomorrow.

[AerysL]

I'm not sure why it happens as it does, but in P1.txt json_verify fails, but P2.txt does not fail, and the only difference in source is the second sed. I'm not familiar enough with the code or sed yet to understand why it happens as it does.
(Note. P{1,2}Ex.txt are just the relevant lines extracted from the P{1,2}.txt)

P1.txt
P2.txt

P1Ex.txt
P2Ex.txt

[rmarquis]

I'm not sure why it happens as it does

Obviously, I cannot merge this PR is the current state. I'll have a look at this issue down the road, but this is very low priority.

[rmarquis]

Done in ff827ea, based on the code of this PR. This was tricky too debug.