Mike Fleetwood authored Mar 18, 2017 and Curtis Gedak committed Jun 02, 2017

For large output a lot of time is used copying capturebuf to callerbuf
to provide a Glib::ustring copy of the buffer for the update callback.
However update callbacks are only used when commands are run to apply
operations by FileSystem::execute_command() and their output is
incrementally displayed in the UI.  Whereas update callbacks are never
used when commands are used to query information via
Utils::execute_command().

Stop performing interim copying of capturebuf to callerbuf when there
are no update callbacks registered as it is unnecessary.

Time to read portions of the recorded fsck.fat output via
fat16::set_used_sectors() and intermediate copies aren't required:

                     1 MiB     10 MiB   122 MiB
    old code :   0.074 sec   1.41 sec   210 sec [3:30]
    new code :   0.063 sec   0.56 sec     6.57 sec

Bug 777973 - Segmentation fault on bad disk