asterisk: introduce a new, multigraph-capable plugin for asterisk.

The new plugin replaces all seven of the old plugins, with a single,
common and collapsed configuration, by drawing multiple graphs with a
single set of transactions to the server.

It also supports autoconf (which was not supported by the old asterisk
plugins), and wildcard/virtual node mode, when monitoring a remote
server.
apache: replace old Apache plugin with new, multigraph-capable one.

The new apache_status plugin provides the previous three graphs as
multigraphs, with a single request to Apache.

It also works as a virtual-node plugin, by querying a remote server.
squid: introduce new Squid plugin to replace the old ones.

Again this plugin uses multigraph and supports virtualnode, and
collapses the five previous squid plugins, reducing the number of
requests coming in for the proxy itself.

Neither output nor configuration ports directly to the new plugin,
unfortunately, but it does allow for saner output and store (in
particular killing cdefs).
plugins: introduce a readfile() function to Munin::Plugin

Especially on Linux where most of the information for the system
status data is read out of /sys or /proc, it's easiest to have a
convenience function that reads a whole file in a scalar variable.
Plugin.pm: introduce a readarray() function

To read one-liners for /sys or /proc
entropy: rewrite plugin in Perl.

This allows us to not have to execute multiple commands to be able to
get the entropy (which could, by themselves, deplete it!).

Additionally, this version fixes the vlabel, and sets the upper limit,
as well as the maximum reading values, to the poolsize.

Since the poolsize is constant for a given kernel, this allows to have
a better, proportioned view of how the entropy varies in the system.
hwmon: introduce a new, multigraph and /sys-based plugin for hardware sensors.

This plugin replaces both the acpi thermal zone plugin and the
lm_sensors based one. It will graph the same data, even though with
different labels (but that involves mostly legacy systems).
uptime: rewrite plugin in Perl

The new version no longer has to fork and use awk to process
/proc/uptime, but handles everything within Perl. Furthermore it
supports dirtyconfig.
load: rewrite plugin in Perl.

The old load plugin looked more like an example plugin that a real
one, but since it's one of the most commonly used ones, it's a good
idea to have this _not_ fork.

The rewritten plugin outputs all three load values, as sometimes the
trend with them helps identifying problems. It also supports proper
autoconfiguration (when /proc is not accessible), and dirtyconfig.

The 5-minutes load average is preserved as 'load', but 'load1' and
'load15' are added.
df: improve plugin and merge with df_inode.

The new plugin is simplified and refactored, but also includes support
for graphing inode usage, if linked as df_inode rather than just df.

Additionally, it supports dirtyconfig so that only one execution of
`df` is needed per update.
procfs: create an aggregated plugin for all data coming from /proc/stat

The list of plugins currently merged in is:

 - cpu;
 - forks;
 - interrupts;
 - swap.

The new plugin, written in Perl, leverages multigraph so that
/proc/stat is only accessed once, and instead of having multiple awk
calls among different plugins getting the same data.

Additional changes to the graph compared to the previous plugins:

 * the cpu graph now output the guest_nice data (which was added to
   the kernel back in 2009);
 * the swaps graph is only generated if /proc/swaps is present as
   not everybody has swaps enabled at all.
Merge pull request #71 from Flameeyes/rewritten-plugins-part-1

Rewritten plugins part 1