pcp update: json pmda

["Frank Ch. Eigler" <fche@xxxxxxxxxx>]

Hi -

Please see git://sourceware.org/git/pcp.git branch fche/json for this ditty:

Author: Frank Ch. Eigler <fche@xxxxxxxxxx>
Date:   Mon Jun 8 20:34:39 2015 -0400

    json pmda: tolerate json array instances that are missing -> PM_ERR_INST
    
    Because of the caching of json array elements in the indom cache
    (/var/lib/pcp/config/pmda/137.*), it is easy to get the pmda machinery
    to recall indom entries that do not currently exist.  Prior to this
    patch, sending those indoms to the pmda fetch-handler resulted in
    needless error messages (and related slowdowns).  We now return the
    correct error (PM_ERR_INST) and don't log anything.


- FChE