Add a lower limit of 0 to postgres database size

This ensures that the graph always starts at 0 in stead of somewhere near the
smallest database size. This makes sure that database sizes are shown
proportionally correct.
Make the postgres_size_ y-axis behaviour configurable.
add the Accept-Encoding header to the wget call

This is necessary to have results comparable to a users browser.
Improve kstat compatibility in sunos if_ plugins

A long time ago, I made the sunos if_ plugins do magic with kstat to only get
the right statistics.  In newer versions of Illumos, some of the pattern
matching magic no longer works (I suspect this is because kstat was converted
from perl script into binary).

This commit fixes the plugins to support the whole spectrum again by moving the
matching magic to awk.
node: support --sconfdir

as is pull request #194 also the plugin configuration dir should be
configurable via a cli switch
Merge remote branch 'pull/136' into devel
Merge remote branch 'pull/218' into devel
Merge remote branch 'pull/219' into devel
Merge remote branch 'pull/221' into devel