Fix thumbnailing so it uses less mem., see vips email

Memory analysis USE TINYSQL OR BDB:
Heap size is too big.
After reading all files in Storage/Music, heap is 6MB
After iTunes retrieves list of songs, heap is 16MB
iTunes retrieval creates 105,427 GNodes (dmap_structure_add)
                 creates 4,217,080 DMAPStructureItem bytes	
                 creates 4,217,080 GNode bytes	
		 creates 356,622 data bytes
2419 songs.
On OpenWRT, heap is 10.6MB, ps ax shows 27,712 RSS, 9.9MB swap used

Entire DMAP structure must be build before serializing and sending. Can we break this up? See _dmap_share_message_set_from_dmap_structure and dmap_structure_serialize.

Strings are copied a few times, but this does not seem to be as big a
problem as the GNode / DMAPStructureItem overhead.
	dmapd:dmapd-daap-record.c: g_value_set_string -> g_value_set_static_string
	libdmapsharing:dmap-structure.c: same as above.
	
==============================================================================

Review:
av-meta-reader-gst.c
av-meta-reader-gst.h
av-meta-reader.c
db-builder-gdir.c
db-builder.c
dmapd-daap-record-factory.c
dmapd-daap-record.c
dmapd-daap-record.h
dmapd-dmap-container-db.c
dmapd-dmap-container-db.h
dmapd-dmap-container-record.c
dmapd-dmap-container-record.h
dmapd-dmap-db.c
dmapd-dpap-record-factory.c
dmapd-dpap-record-factory.h
dmapd-dpap-record.c
dmapd-dpap-record.h
dmapd.c
dmapd.h
libmeta-gst.la
photo-meta-reader-graphicsmagick.c
photo-meta-reader-graphicsmagick.h
photo-meta-reader.c
usage_dmapd.c
util.c

*** Dynamically adjust database when files are added to directories.

*** Support SMIL playlists.

*** Fix seeking (see libdmapsharing TODO)

Fedora package of dmapd (submitted).
	
Migrate command line parsing to dmapd.xml.

Update documentation in dmapd.xml.

GStreamer:
	- DV State change failed for /shared/Storage/Movies/2006 1707 Oak/2006_house_condition_5.dv Bugzilla #569924
	- Break up gstreamer packages (see OpenWRT example):

Why do some albums (e.g.: 2008 Landscape) appear blank?
