This does the actual work of going out and checking the mirror status. In
short, it polls every active mirror URL for the 'lastsync' file and then
records the appropriate details. These include the contents of that file,
how long the total time to retrieve took, and any errors encountered.
In order to finish up a bit faster, we spawn several threads to do the
actual work. This parallelization allows the whole check process to take
around 30 seconds rather than several minutes.
Signed-off-by: Dan McGee <dan@archlinux.org>
