Add some paranoia to wtperf's copying and randomizing of values.

refs #1032
Merge branch 'develop' into wtperf-randomize-value
Allow all byte values when wtperf randomizes its values: we will occasionally generate "special" values such as the ones that start with the LSM tombstone.

refs #1032
Fix the pareto calculation in wtperf: __wt_random returns values up to UINT32_MAX, not RAND_MAX.

found when testing for #1032
Factor out the code to generate keys in wtperf, include the trailing NUL in the size.
Merge pull request #1035 from wiredtiger/wtperf-randomize-value

Add some paranoia to wtperf's copying and randomizing of values.