Features
* librrd is now fully thread-safe. librrd_th is gone
* make lua bindings work with lua 5.1
* configure option to disable doc building --enable-docs=no
* new CDEF function SMIN: a,b,c,3,SMIN -> min(a,b,c)
* new CDEF function SMAX: a,b,c,3,SMAX -> max(a,b,c)
* new CDEF function STDEV: a,b,c,3,STDEV -> stdev(a,b,c)
* new CDEF function POW: a,b,POW -> a**b
* new CDEF function PERCENT: a,b,c,95,3,PERCENT -> find 95percentile of a,b,c
* re-introducted --showtime option on rrdxport
* be more careful in determining the locales idea of first day of the week
* lots of spelling fixes all around
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