### Please describe the problem.

I just started git-annex, and I can hear the fan of my CPU. That doesn't happen unless the CPU is maxed, and indeed:

[[!format txt """
top - 10:09:53 up 2 days, 13:13, 10 users,  load average: 2,49, 2,41, 1,59
Tasks: 306 total,   3 running, 302 sleeping,   0 stopped,   1 zombie
%Cpu(s): 57,2 us,  7,9 sy,  1,2 ni, 32,1 id,  1,3 wa,  0,0 hi,  0,3 si,  0,0 st
KiB Mem:   8162960 total,  7480272 used,   682688 free,  1107616 buffers
KiB Swap:  4022268 total,    23384 used,  3998884 free,  3469028 cached

  PID USER      PR  NI  VIRT  RES  SHR S  %CPU %MEM    TIME+  COMMAND
27841 anarcat   20   0  191m  45m  20m S  92,3  0,6   4:32.68 /usr/local/bin/git-annex webapp
"""]]

### What steps will reproduce the problem?

I am not sure. I just started the webapp, and it seems to be scanning two huge repositories (160GB and 800GB) with lots of files. The larger one is also in the process of being sync'd to the backup drive.

### What version of git-annex are you using? On what operating system?

My usual bastard build from hell:

[[!format txt """
git-annex version: 5.20131109-gf2cb5b9
build flags: Assistant Webapp Pairing Testsuite S3 WebDAV Inotify DBus XMPP DNS Feeds Quvi TDFA CryptoHash
key/value backends: SHA256E SHA1E SHA512E SHA224E SHA384E SKEIN256E SKEIN512E SHA256 SHA1 SHA512 SHA224 SHA384 SKEIN256 SKEIN512 WORM URL
remote types: git gcrypt S3 bup directory rsync web webdav glacier hook
local repository version: 3
default repository version: 3
supported repository versions: 3 5
upgrade supported from repository versions: 0 1 2 4
"""]]

### Please provide any additional information below.

Note that I had to close the chromium tab that was displaying the actual webapp UI, because that was taking another 50% of a CPU (I have a dual core).

Note also that things calmed down since git-annex started transfering larger files - the webapp only takes 75% of the CPU now. ;) And chromium is negligible. But there clearly seems to be a degenerate case where a lot of small files get transfered that seem to freakout the web UI. -- [[anarcat]]

Oh, and just copying the files using `git annex copy --to backup` doesn't use 100% of the CPU.