Added nfs4 support for linux
Add support for recent 4.0-only configurations
fix typos in comments
reduce switch statement
Add support for monitoring lm_sensors' "power" sensors

The patch shall probably be extended to include additional sensor names in
future. My servers, however, use "power1" for all of the readings, so I'm not
making that change now.
Add postgresql writer option to skip older values.
Fix for number of nfs40 client fields on linux >=3.5
add more innodb metrics
submit mysql_bpool_bytes as gauge
add a test suite
replace Regexp::Common with core Scalar::Util
clean up Perl style a bit

- Remove some superfluous parenthesis clutter
- Shorten a lot of single-line conditionals using postfix constructions
- Merge variable declarations
- Use $class/$self instead of $pkg/$obj as is customary
- Remove quotes around literal hash keys
refactor common query-response code
add listval_filter method and corresponding tests

Rationale:
A frequent use case for LISTVAL is to retrieve a list of resources for a certain
host or host group that is not known in advance, such as when the hosts have
different disks installed. Using the existing listval() method,
Collectd::Unixsock retrieves the entire list, parses each entry into a hash and
returns the list, only to have the caller throw away the vast majority of
entries immediately. listval_filter() allows the caller to pass any attribute
that can be passed to getval() and filters the list of resources retrieved from
the socket before parsing it, resulting in a large speedup.
The current implemntation has some code duplication, although listval() could be
implemented as a small wrapper around listval_filter() with just a few percent
speed penalty due to the extra dynamically built regexp.
Added support for the last two additional columns in add-linux-io-time
missed the output_name
configure: add varnish4 presence detection
varnish: bare minimum changes to support varnish4
varnish: adapt to metrics renames & deprecations in varnish4

Summary of changes:
- connections: "accepted" & "dropped" are now found in the session section
- dirdns: doesn't exist in varnish 4 anymore
- objects: "n_obj*" were removed from varnish 4
- ban: "obj", "req" & "completed" bans were added. As a lot of new
  "tested" metrics are available, so we only collectd the overall total
  now
- session: metrics from "connections" and "threads" categories were
  moved here
- struct: "n_sess*" were removed
- totals: new, more detailed *bytes metrics were made available
- threads: new metrics were made available. "queued" was moved the
  session section.
varnish: add a couple of metrics available both in V3 & V4