Log Message:
Changes 1.5.5:
Bugfixes
--------
* fix JSON output in xport with legend and gprint blocks
* fix parse_time mutex unlocking in the error case
* don't crash on invalid variable names in CDEF
* add mutex locking in rrdc_fetch
* fix buffer overflow in rrd_restore
* shorten test precision to 7 digits ...
* never exit from a library function
* buffer overflow in rrd_restore.c