tlmgr and context cache building

[Karl Berry]

Some of you will remember the voluminous output to the terminal the last
time there was a tlmgr update involving context (the re-integration of
mkiv thanks to Siep).

I just made some changes to tlmgr and install-tl, etc., to try to
redirect all that output from the context cache updates into log
files. (tlmgr revision 69653)

We'll see what happens tonight. Just wanted to send a heads-up since I
won't be online again until after most people doing daily updates have
already seen the result, good or bad :). --happy updating, karl.