Summary:
to debug the sql performance we need a to trace the sql queries. This hacky module
facilitates that need.
Test Plan:
[mitrandir@dev3277 fbsource (92e442f)]$ xhg --config sqldirstate.tracefile=trace st
? fbcode/eden/x.py
[mitrandir@dev3277 fbsource (92e442f)]$ cat trace |arc paste
Reading paste from stdin...
P56530356: https://phabricator.intern.facebook.com/P56530356
Reviewers: #mercurial, ttung, durham
Subscribers: mjpieters
Differential Revision: https://phabricator.intern.facebook.com/D3626545
