Included memory usage per VM

Included all the metrics about the actual memory used by VMs (as
returned by libvirt.virDomainMemoryStats)
Collect drbd statistics on linux
configure.ac: Include liblvm2app in configuration summary
lvm: Change unused return value to void
lvm: Ignore virtual volumes

The sum of the sizes reported by a volume group should equal the size
of the volume group.  Virtual volumes do not directly correspond to
allocated storage (and, in fact, may be larger than the entire volume
group), so must be ignored.
lvm: Report used/free space for thin pools and thick snapshots

Thin pools and traditional snapshot volumes fill up as I/O is performed
to their associated thin volumes or origins.  When they run out of free
space, things break, so it's useful to monitor their disk utilization.

Add new plugin instances for thin pool data LVs, thin pool metadata LVs,
and thick snapshot LVs, each with "used" and "free" type instances.
lvm: Fix segfault if a VG contains no LVs
lvm: Avoid lvm_lv_get_attr()

It is only available in liblvm2app >= 2.02.99, which is not in Debian
Wheezy.
configure.ac: Check for newest liblvm2app symbol needed by lvm

lvm_lv_get_property() was added in 2.02.75.
Warn if ttl is out of bounds
network: set ttl before opening server sockets

If TimeToLive is defined in collectd.conf after Server options, the
net_config_ttl value is updated after network_config_add_server and
the desired ttl is not used.
drbd plugin: replace atoi with strtol
drbd plugin: expand comments
drbd plugin: Relicense to MIT license
per-url intervals for curl_json
Merge pull request #654 from timl/fix_ttl_order

Fix ttl order
Fixing misplaced block in documentation.
Merge pull request #687 from txaj/fix-doc-postgresmodule-sslmode

Fixing misplaced block in documentation.
Merge pull request #685 from teftin/curl-json-per-url-interval

per-url intervals for curl_json
build: remove obsolete reference to bundled libiptc

Libiptc was removed 3 years ago in 99364c70, so this option to
./configure isn't of any use anymore.