contrib/jemalloc

I have the current version of jemalloc integrated into libc as contrib/jemalloc:

	http://people.freebsd.org/~jasone/patches/jemalloc_20120404b.patch

This is the first update to FreeBSD's jemalloc in over two years, and the differences are huge (faster, better introspection, hopefully fewer bugs).  This has been stable for me across numerous buildworld/installworld iterations, as well as when running several benchmarks.  There's a bugfix to openpam in the patch that des says will be obsoleted by the next vendor import, so I'm planning to let that settle before committing.  In the meanwhile, I'm hoping for some review sanity checks on the following aspects of the patch:

* Are the symbol versioning specifications right, and are the compatibility symbols for _malloc_options and _malloc_message workable?

* Is it acceptable to check this in directly to trunk without using a vendor branch?  For the import workflow I have planned, a vendor branch would just be extra work with no benefit that I can see.

* Is the light editing of the jemalloc manual page sufficient?  Keeping the changes minimal will make regular imports less work, but the result is less tailored to FreeBSD.

* Will the utrace feature be missed?  I removed it some time ago, mainly because traces are impossibly large for most real-world use cases.

Thanks,
Jason