The C++11 driver upgraded to the 1.5.0-rc0 release on its 3.1-dev branch, and several of our builders are now red

• Before the upgrade: https://evergreen.mongodb.com/version/57dec65d3ff1222d3400021f
• After the upgrade: https://evergreen.mongodb.com/version/57dec7d63ff1222d34000223

The ASAN and Valgrind issues seem to be consistent, and point to _mongoc_cursor_cursorid_init and _mongoc_cursor_new.

Sync the C driver back to f4cfb6eb708913a1795090faecbe3196fb7b5c58 and the C++11 driver test no longer fails under valgrind. Checking out f6c6085076415150ad97fa4d0950ea991d420971 adds memory leaks. Then checking out f066f14e7c9862a843f54700c3f3f36fe11fba80 seems to change the type of leaks, but they are still present