provenance: Switch from glibc malloc to jemalloc

The three executables building the final provenance index (contents-in-directories, contents-in-revisions-without-frontier, and frontier-directories-in-revisions) make lots of small allocations when concatenating paths.

With glibc malloc on a 96 threads system, this was causing 1/3 to 2/3rd of the time in a lock.

Switching to jemalloc brings a 6x speedup overall.

While not strictly needed, this commit switches other provenance executables to jemalloc as well, for consistency (so profilings aren't inconsistent from one to the other).