Fix computation of devtools Idle time

We were calculating the end-of-processing time using the *start* time of
the event that finished last, when we should instead be using the *end*
time of that event.
Merge pull request #277 from aroben/patch-1

Fix computation of devtools Idle time
Fixed #279 - added a fallback where we poll the main browser window text from c++ to get the title in case we did not get it directly from the browser.  The downside is that we poll on a 100ms timer so the accuracy isn't quite as good as an active callback but it's much lighter weight than polling in the browser.
Updated the navigation counter to include "andwait" steps.
Merge branch 'master' of github.com:WPO-Foundation/webpagetest
Updated the startup settings loading to keep trying with no timeout
Fixed #281 - Added an install check to make sure the dat directory is writable (and updated the documentation).
Fixed #280 - Put protection in place to make sure to only use curl when it is installed and added fallbacks where possible
Fixed #268 - reset the priority on a test resubmit
wptdriver 2.15.0.183
pagetest 2.15.0.379
Updated flash player
Fixed the csv processing so it will use the existing file if it is present.
Updated version to 2.15
Fix bug where statistical comparisons with p-values rounding to zero had no significance information.
Removed dead code
Added the benchmark reprocessing script
Separate out graph_page_data.php JS into separate file
Merge master into ab
Move logic for going from 1-tailed to 2-tailed p-value into PHP