Add ability to create multiple tables to wtperf.

Implemented by new table_count configuration option. Wtperf will create
table_count number of tables, and populate each with the full set of data,
then workload operations will be spread randomly over the set of tables.
Fix compiler warning re: uninitialized variable.
Add a script that can graph wtperf monitor using NVD3.
Fix scale on wtperf NVD3 graph.
Update gnuplot wtperf graphing script to work again.
Add a wtperf option to wtstats NVD3 graphing script.

This takes adds wtperf monitor statistics to the WiredTiger statistics
plots. Assumes that the statistics file(s) are in the wtperf directory,
also currently requires that --abstime argument is used.
Add support for --abstime argument to wtperf NVD3 graph script.
Merge branch 'develop' into wtperf_monitor_nvd3

Conflicts:
	tools/wtperf_graph.py
Fix a remnant from the merge.
Remove unnecessary every clause from gnuplot script.
Merge pull request #872 from wiredtiger/wtperf_monitor_nvd3

Add a script that can graph wtperf monitor using NVD3.
Merge pull request #867 from wiredtiger/wtperf-multi-table

Add ability to create multiple tables to wtperf.