asyncd: ident help options
asyncd: adding support for non std default rate

Adding an option for a very simple overriding the default update_rate value.
This enables a very easy 1 min polling setup.
snmp__if_multi: get the interface alias from SNMPv2 if it is defined
plugins/http_loadtime: add specific user-agent

I spent a bit of time looking what was calling http://127.0.0.1/ on
my server with the default wget user agent string.

Looked around a bit more and realized it was the Munin HTTP load
time plugin. Adding this simple user agent string so sys-admins
will know what it is when they look at their logs.
Add doc for missing node directives in munin.conf
Set "the munin project and its contributors" as authors, and use that in the copyright string.
Add node definitions to the munin.conf reference
master: update test for config default

Commit 1aec747c10f0d5077842294ca351b918b77fb1e9 added a
default for graph_strategy. test has be updated.
node: use a 5% tolerance for timings tests

If the tests are done on a VM, the timings are not precise enough. So increase the error margin to cope with it.

It was at 0.5%, and this commits sets it at 5%
Merge branch 'async-enh' into devel

Conflicts:
	node/_bin/munin-asyncd.in
doc: adding some context to async
master: add feature to disable graph_total

According to Philipp Niemann on the mailing-list :

    This is a new configuration option for munin.conf to deactivate the graphing
    of total values on a per-plugin scope.

    So currently one has to change the plugin itself, which is clumsy and only
    lasts till the next update of plugins.

Once set in the plugin code, no value can deactivate it.  This makes the
special value "undef" deactivate it. It can therefore be overriden properly
via munin.conf.

Closes: #827
p/http_loadtime: avoid temporary files

As caluml reported :

    I believe this patch makes it simpler, as it doesn't involve writing files.
    We have had issues in our environments whereby the temp files don't get
    removed.  I'm not sure why, but it seems unnecessary to write them at all.

Closes: #1133
p/snmp__if_: support ifHighSpeed

Patch thanks to tarnell :

    Currently, snmp__if_ doesn't support interfaces faster than 4.3Gbps, because
    it's limited to the 32-bit ifSpeed field.  This patch extends it to use
    ifHighSpeed, which returns the speed in Mbps and so supports faster interfaces.

Closes: #1037
p/snmp__if_: accept interface num with leading 0

This enables to have nicely indented symlinks.

Closes: #1018