[PATCH v3] 0/4 fsmonitor fixes

Updates since v2:

 - Fix tab which crept into 1/4

 - Fixed the benchmarking code in the commit message in 2/4 to just
   always load JSON::XS -- the previous version was the version where
   I'd broken that to force loading of JSON::PP.

 - Remove the --no-pretty from the t/ version of query-watchman in
   2/4; I don't know how I messed up diff'ing the file previously, but
   if there are already differences, it makes sense to let them slide.