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