[Tracker] Review request: extractor-dbus-fd

[Adrien Bustany <abustany gnome org>]

Hello list,

I ported the communications between tracker-extract and
tracker-miner-fs to use a pipe (DBus FD passing). So far, the FS miner
has been crunching files fine here, but I guess it could withstand some
more testing.
I didn't observe a spectacular speedup (7% on a 4400 files, 3.7G folder
containing mainly files with plain text content), but at least it
should offload DBus.
So far I didn't replace the GetMetadata method, I rather added a
GetMetadataFast. I don't think keeping the "old" method constitutes a
big overhead, and it makes backwards compat for DBus 1.3 much easier.

Cheers

Adrien